Question

Recently physicians have determined that stomach ulcers are not caused by stress, alcohol, or rich foods, but a bacterium that dwells in the mucous lining of the stomach.

• A. Not caused by stress, alcohol, or rich foods, but
• B. Not caused by stress, alcohol, or rich foods, but are by
• C. Caused not by stress, alcohol, or rich foods, but by
• D. Caused not by stress, alcohol, and rich foods, but
• E. Caused not by stress, alcohol, and rich foods, but are by

Answer 1

Answer: (C)

Caused not by stress, alcohol, or rich foods, but by

The give sentence lacks parallelism. The sentence talks about a recent conclusion that physicians have come to- they have determined that ulcers are : 1. NOT caused by stress, alcohol, or rich foods

2. BUT a bacterium that dwells in the mucous lining of the stomach

The sentence therefore has a list of two elements joined by the idiom 'not....but'. These two elements need to be parallel. However, 'caused by stress...' and 'a bacterium' are not parallel. As we can see, in option C the use of 'by stress...' and 'by bacterium...' transforms the sentence into one that confirms the required parallel structure as both of them are prepositional phrases that play the same role in the sentence. None of the other options do this. Therefore, B is the correct answer.