Understanding Grammatical Errors in Sentences

Let's examine the given sentence and identify if there is any grammatical error in the marked parts.

The sentence is:

Sleep is indispensable for maintaining immunological (1)/function, which is a key to prevent (2)/and recover from infectious diseases (3)/ .No error (4)

Analysis of Each Part

Let's break down each part:

1. Sleep is indispensable for maintaining immunological function: This part appears grammatically correct. 'Indispensable for maintaining' is a valid construction.
2. which is a key to prevent: The phrase 'a key to' is typically followed by a noun or a gerund (the -ing form of a verb). Here, it is followed by the base form of the verb 'prevent'. This should ideally be 'a key to preventing'.
3. and recover from infectious diseases: This part follows from 'which is a key to prevent (2)/ and recover from infectious diseases (3)'. It links 'prevent' and 'recover'. For parallelism, if 'prevent' were correctly 'preventing' after 'a key to', then 'recover' should also be 'recovering'. The structure should be "a key to preventing and recovering from...". Since 'recover' is used as a base verb here, and it should be a gerund ('recovering') to match the required form after 'a key to' and for parallelism with 'preventing', this part contains an error.
4. No error: This is chosen if no error is found in parts (1), (2), or (3).

Identifying the Specific Error Location

The phrase "a key to" requires a noun or a gerund. Therefore, part (2) should be "a key to preventing". Following the principle of parallelism, if the first item after "to" is a gerund ("preventing"), the second item ("recover") linked by "and" should also be a gerund ("recovering"). While the initial error in using a base verb after "a key to" occurs in part (2), the error in parallelism and the incorrect form ("recover" instead of "recovering") exists in part (3).

The error lies in part (3) because the verb 'recover' is not in the correct gerund form ('recovering') needed for parallelism with the required structure following 'a key to'. The correct phrasing would be "which is a key to preventing and recovering from infectious diseases". Thus, the use of 'recover' in part (3) constitutes an error.

Conclusion

The error is found in part (3) of the sentence. The word 'recover' should be 'recovering' to maintain parallelism with the gerund form required after 'a key to' and to correctly complete the phrase "a key to preventing and recovering from...".