Bunuel wrote:
Ignoring the admonitions of his staff, the chief financial officer accepted the advice of the consulting company because he believed that the standardized accounting procedures would prove not only inexpensive but reliable indicators of economic performance.
(A) he believed that the standardized accounting procedures would prove not only inexpensive but
(B) the standardized accounting procedures will prove both inexpensive and also
(C) he believed the standardized accounting procedures would prove themselves to be both inexpensive and
(D) he believed that the standardized accounting procedures would prove to be both inexpensive and
(E) standardized accounting procedures will prove his belief that they are both inexpensive and
sentence is in past tense. "CFO believed" is in past so what did he believe should also be in past. Past Future for "Will" is "WOULD"
I think core of sentence will be CFO accepted the advice because he believed that XYZ.
(A) he believed that the standardized accounting procedures would p
rove not only inexpensive but --- Not Only + But Also. Also is missing here
(B) the standardized accounting procedures will prove both inexpensive and also --- believe is missing.
(C) he believed the standardized accounting procedures would prove
themselves to be both inexpensive and--- extra word. I think "believed that" is better than alone believed
(D) he believed that the standardized accounting procedures would prove to be both inexpensive and --- Correct
(E) standardized accounting procedures will prove his belief that they are both inexpensive and --- believe is missing.