Official Solution:Shortly after sunset there were juddering green stabs of lightning to the south, but by a quarter to one in the morning there had been nothing in the warm, wet July air over Cape Canaveral but a thin patchwork of moonlit cloud.A. were juddering green stabs of lightning to the south, but by a quarter to one in the morning there had been nothing in the warm, wet July air over Cape Canaveral but
B. has been juddering green stabs of lightning to the south, but by a quarter to one in the morning there is nothing in the warm, wet July air over Cape Canaveral but
C. had been juddering green stabs of lightning to the south, but by a quarter to one in the morning there is nothing in the warm, wet July air over Cape Canaveral but
D. is juddering green stabs of lightning to the south, but by a quarter to one in the morning there was nothing in the warm, wet July air over Cape Canaveral but only
E. have been juddering green stabs of lightning to the south, but by a quarter to one in the morning there is nothing in the warm, wet July air over Cape Canaveral except
For using past perfect the later past event does not need to be expressed with a Simple Past tense verb. One could just use a date or another time reference. Using this construction, this sentence is set up: first clause expresses an early action in Simple Past. Then, a second clause expresses a later action in Past Perfect to indicate continued effect (by a still later past time).
A. “Quarter to one” is the time reference here before which another verb “had been” took place. Therefore the verb “had been” is used correctly in the past perfect to depict that the sky was already clear before quarter to one and the effect of the verb was still there at quarter to one.
B. Present perfect indicates an action whose effect is still present. However the effect of the occurrence of juddering green stabs of lightning is no longer present and hence the use of present perfect “has been” is wrong. Moreover “has been” is a singular verb and does not correspond to the plural subject “stabs”.
The simple present “is” is wrong. The present is not depicted, but the past before quarter to one is indicated by the verb “had been” - the effect of that verb still existed at quarter to one and hence the use of past perfect is required.
C. The verb “had been” is wrongly used in past perfect tense - there is no corresponding past event or time reference that bears on this verb.
The simple present “is” is wrong. The present is not depicted, but the past before quarter to one is indicated by the verb “had been” - the effect of that verb still existed at quarter to one and hence the use of past perfect is required.
D. The verb “is” is in simple present tense, but the verb occurred in the past - hence use of simple present tense is wrong.
Use of simple past “was” is wrong - past perfect is required to depict an action that occurred before the time reference “by quarter to one” and whose effect was still present at “quarter to one”.
E. Present perfect indicates an action whose effect is still present. However the effect of the occurrence of juddering green stabs of lightning is no longer present and hence the use of present perfect “have been” is wrong.
Answer: A