Telomerase is an enzyme that is produced only in cells that are active

This question has been giving many people a lot of trouble, and the truth is that the reason there are so many doubts is that the question has issues, as some of the wording does not quite clearly state what the question's creator felt that it states. So let's define what the issues are.

First let's define what they are not. Answer choices A, D and E, are fine. Each of them says something that clearly cannot be inferred from what the prompt says.

A does not have to be true. There could be all manner of differences between cancerous cells and cells that are not actively dividing.

D cannot be inferred, as what the prompt say about bone marrow does not clearly indicate anything about the rate at which bone marrow cancer grows.

E cannot be inferred as the prompt does not indirectly or directly support any conclusions about relative levels of telomerase production. It merely provides a binary set of situations, cells in which telomerase is produced and cells in which telomerase is not produced.

Ok so, with A, D, and E out, we are left with the two problematic answer choices.

First let's talk about B, "In children, the only body tissues from which telomerase is absent are those in which cells are not rapidly dividing."

Since C is the OA, the creator of this question clearly felt that B cannot be inferred from the prompt, and here is the logic underlying that stance.

For all we know, while the prompt says that telomerase is only produced by cells that are dividing, it is possible that not all cells that are dividing produce telomerase. That cells that are dividing may not produce telomerase seems possible, and this logic means that B cannot be inferred.

However, there are aspects of the wording of the prompt that could be taken to indicate that actually all dividing cells produce telomerase.

The prompt says, "Bone marrow is an exception to this rule, however, since even in adults, bone marrow cells continually divide to replace old blood cells." The prompt also says, "Cancers are another exception, because their cells are rapidly dividing."

The implication that one could take from those statements is that SINCE BONE MARROW CELLS AND CANCER CELLS DIVIDE, THEY ARE EXCEPTIONS. The prompt does not say that since they divide they CAN BE exceptions. It say that since they divide they ARE exceptions, which can be taken to mean "SINCE THEY DIVIDE, THEY PRODUCE TELOMERASE."

That somewhat reasonable interpretation of the meanings of the sentences in the prompt could in turn be taken as implying that CELLS THAT DIVIDE PRODUCE TELOMERASE, which supports B.

I believe that that analysis partially explains why B is being chosen by so many people.

Now let's look at C, "The presence of telomerase in bone marrow is no indication of bone marrow cancer."

The issue in C is similar to the issue in B, actually.

Just as B does not say CAN BE AN EXCEPTION, C does not say, IS NOT NECESSARILY AN INDICATION.

C says that telomerase in bone marrow is NO indication of cancer. That's an extreme statement, as telomerase in bone marrow could be coming from cancerous cells. I realize that I am playing with subtle differences, but I think that if C were worded even "The presence of telomerase in bone marrow is NOT AN indication of bone marrow cancer," C would be slightly clearer.

So if the wording in the prompt regarding the bone marrow and cancer exceptions were just slightly clearer, and if a couple of words in C were changed in order to increase clarity, this question would perhaps go from 700 level to 600 level.