Good questions, Elena

1. ...people show... in their ...., the more likely THEY are.... in the arteries of THEIR hearts.

If you notice, people is pointed to twice outside the underlined portion by "Their". This definitely justifies the usage of they to point out the calcium deposits occur to those same people. Anything else would actually introduce ambiguity

2. There is a form of "be".
eg. There is a possibility that the world could end in 2012.
or, It is likely that there will be....

It is general, and seems to say that whatever follows simply exists. (Atleast in this sense, ofcourse you could also say "I'm going there" to point out WHERE you are going )

In this sentence, "there" won't work. "the more likely there are to be" would have to have been "the more likelihood there is ..." The noun form is necessary. You can't use an adverb with there, if that makes sense.

I'm sure these doubts will get dispelled as you read more GMAT questions. Good luck!

substantial reason required to remove E

hi, instructors, in my view, chioice D, add some information.... the original sentence says " calcium deposits are more likely to be..." while in choice D. it's" they are to have calcium deposits.." i think we add the word " they" here, which doesn't show in the original sentence...so it distorts the meaing... please correct me...

I think the only choice which seems idiomatically correct is D, of course.
the formation is -> the more X people show ... the more likely "they" ( refers to people) are to Y.