HI

in the below question,the official answer is C but I have a doubt that since the whole para is written in past tense than how c which brings in present tense i.e "is",can be correct.


Q-Researchers agreed that the study of new treatments for heart attack patients was extremely important but more research was needed to determine that balloon angioplasty preceded with ultrasound was or was not any better for heart attack patients than the balloon procedure by itself.

A. more research was needed to determine that balloon angioplasty preceded with ultrasound was or was not any better for heart attack patients than
B. more research was needed for determining whether or not balloon angioplasty preceded by ultrasound is any better for heart attack patients than is
C. that more research was needed to determine whether balloon angioplasty preceded by ultrasound is any better for heart attack patients than
D. that more research was needed to determine that balloon angioplasty preceded with ultrasound was any better for heart attack patients than
E. that more research was needed for determining that balloon angioplasty preceded by ultrasound is or is not any better for heart attack patients than is


My analysis-->I understand that choice can be decided by the option of

Parallelism i.e use of "agree that....but that...."(a & b out)

use of "preceded by" vs "preceded with"(d out)

use of "needed for determining" vs "needed to determine"(e out)

but Why here use of present tense in the option c is correct?why not we select d as an answer.Please uggest