Question

Fill in the blank with the correct tense in the following sentence:

Even the early doctors knew that washing hands _____ infection.

• A. preventing
  
• B. will have been preventing
  
• C. prevents
  
• D. None of the above
  

Answer 1

The correct option is C prevents

Option C is correct. The past tense in the main clause (knew) can be followed by a present tense in the subordinate clause (prevents), when the subordinate clause expresses a universal truth. We know that washing hands to prevent infection is a universal truth and thus, can be written in the present tense.

Option A is grammatically incorrect.

Option B is incorrect as "will have been preventing" is future perfect continuous. This tense is used to describe an action which will be in progress over a period of time and that will end in the future. In the given sentence, there is no indication of when the action of washing hands will end.

Option D is incorrect since the answer is C.