Tmoni26 wrote:To screen women for colorectal cancer, the use of either colonoscopy or flexible sigmoidoscopy is acceptable although a recent study shows that this is the preferred method

A. or flexible sigmoidoscopy is acceptable although a recent study shows that this
B. and flexible sigmoidoscopy is acceptable although a recent study shows that colonoscopy
C. or performing flexible sigmoidoscopy is acceptable although a recent study shows that the former
D. or flexible sigmoidoscopy is acceptable although a recent study shows that the former
E. or flexible sigmoidoscopy is an acceptable method although a recent study shows that colonoscopy

In A, this lacks a clear referent.
Eliminate A.

In B, either...and is unidiomatic.
The correct idiom is either X or Y.
Eliminate B.

Either X or Y must serve to connect PARALLEL FORMS.
C: either colonoscopy or performing flexible sigmoidoscopy
Here, colonoscopy (noun) and performing flexible sigmoidoscopy (VERBing + direct object) are not parallel forms.
Eliminate C.

E: the USE...is an acceptable METHOD
Here, use and method seem redundant.
Eliminate E.

An introductory infinitive modifier (to + VERB) should serve to express the intent of the SUBJECT of the following clause.
SC42 in the OG13:
To develop more accurate population forecasts, demographers would have to know a great deal more than they do now.
Here, to develop (an introductory infinitive modifier) correctly serves to express the intent of demographers (the subject of the following clause).
Conveyed meaning:
DEMOGRAPHERS intend TO DEVELOP more accurate population forecasts.

OA: To screen women for colorectal cancer, the use...is acceptable.
Here, to screen (an introductory infinitive modifier) seems to refer to the use (the subject of the following clause), implying that THE USE intends TO SCREEN women.
Since the use cannot have an intent, this sentence is not viable.
I would ignore this SC.