GMAT Sentence correction
It seems the question above may make use of parallel strategy but in fact other tools are more effective:
1. tense: 'are usually reliable' so that 'A' should be eliminated due to 'could not be foreseen'.
2. pronoun: GMAT grammar doesn't fancy pronoun, which is often trick in questions. In this way, we can see the only choice without 'they' is option 'B'.
3. smart tool : 'they had' in A, C, D, E is controversial to the present tense used in the first half of the sentence. Thus 'B' is an obvious choice we can see.