Choice E, the best answer, uses constructions that are parallel to some propose', others suggest. . . , and
still others are calling ....
Choices A and B immediately lose the parallel construction, and also produce sentence fragments, by shifting to by suggesting ... and by calling ....
Choice B starts like choice A and then shifts back to the verb call, losing the parallel with the second part (by suggesting).
Choices C and D correctly begin the second part of the parallel by using suggest.
Choice C, however, introduces the nonidiomatic for decreasing, which creates some difficulty in meaning.
Choice D loses parallel construction in the third part by shifting to by calling.
The main thing in this question is to find parallel constructions.
Look:
some propose.............
others suggest........,
and still others are calling.......
