This is one of many issues about which the Church has no official position. As President J. Reuben Clark taught under assignment from the First Presidency:

Here we must have in mind—must know—that only the President of the Church, the Presiding High Priest, is sustained as Prophet, Seer, and Revelator for the Church, and he alone has the right to receive revelations for the Church, either new or amendatory, or to give authoritative interpretations of scriptures that shall be binding on the Church....

When any man, except the President of the Church, undertakes to proclaim one unsettled doctrine, as among two or more doctrines in dispute, as the settled doctrine of the Church, we may know that he is not "moved upon by the Holy Ghost," unless he is acting under the direction and by the authority of the President.

Of these things we may have a confident assurance without chance for doubt or quibbling.^[1]

Harold B. Lee was emphatic that only one person can speak for the Church:

All over the Church you're being asked this: "What does the Church think about this or that?" Have you ever heard anybody ask that question? "What does the Church think about the civil rights legislation?" "What do they think about the war?" "What do they think about drinking Coca-Cola or Sanka coffee?" Did you ever hear that? "What do they think about the Democratic Party or ticket or the Republican ticket?" Did you ever hear that? "How should we vote in this forthcoming election?" Now, with most all of those questions, if you answer them, you're going to be in trouble. Most all of them. Now, it's the smart man that will say, "There's only one man in this church that speaks for the Church, and I'm not that one man."

I think nothing could get you into deep water quicker than to answer people on these things, when they say, "What does the Church think?" and you want to be smart, so you try to answer what the Church's policy is. Well, you're not the one to make the policies for the Church. You just remember what the Apostle Paul wrote to the Corinthians. He said, "For I determined not to know any thing among you, save Jesus Christ, and him crucified" (1 Corinthians 2:2). Well now, as teachers of our youth, you're not supposed to know anything except Jesus Christ and Him crucified. On that subject you're expected to be an expert. You're expected to know your subject. You're expected to have a testimony. And in that you'll have great strength. If the President of the Church has not declared the position of the Church, then you shouldn't go shopping for the answer.^[2]

This was recently reiterated by the First Presidency (who now approves all statements published on the Church's official website):

Not every statement made by a Church leader, past or present, necessarily constitutes doctrine. A single statement made by a single leader on a single occasion often represents a personal, though well-considered, opinion, but is not meant to be officially binding for the whole Church. With divine inspiration, the First Presidency...and the Quorum of the Twelve Apostles...counsel together to establish doctrine that is consistently proclaimed in official Church publications. This doctrine resides in the four “standard works” of scripture (the Holy Bible, the Book of Mormon, the Doctrine and Covenants and the Pearl of Great Price), official declarations and proclamations, and the Articles of Faith. Isolated statements are often taken out of context, leaving their original meaning distorted.^[3]

In response to a letter "received at the office of the First Presidency of the Church of Jesus Christ of Latter-day Saints" in 1912, Charles W. Penrose of the First Presidency wrote:

Question 14: Do you believe that the President of the Church, when speaking to the Church in his official capacity is infallible?

Answer: We do not believe in the infallibility of man. When God reveals anything it is truth, and truth is infallible. No President of the Church has claimed infallibility.^[4]

There is more material on official doctrine in the Church in this link.

Notes

1. ↑ J. Reuben Clark, Jr., "Church Leaders and the Scriptures," [original title "When Are the Writings or Sermons of Church Leaders Entitled to the Claim of Scripture?"] Immortality and Eternal Life: Reflections from the Writings and Messages of President J. Reuben Clark, Jr., Vol, 2, (1969-70): 221; address to Seminary and Institute Teachers, BYU (7 July 1954); reproduced in Church News (31 July 1954); also reprinted in Dialogue 12/2 (Summer 1979): 68–81.
2. ↑ Harold B. Lee, Teachings of Harold B. Lee (Salt Lake City, Utah: Bookcraft, 1996), 445.
3. ↑ LDS Newsroom, "Approaching Mormon Doctrine," lds.org (4 May 2007)
4. ↑ Charles W. Penrose, "Peculiar Questions Briefly Answered," Improvement Era 15 no. 11 (September 1912).