Pick the part of the sentence that contains an error.
(a) He does not listen to (b) what I say, (c) although I am advising him for a long time.
a) (a)
b) (b)
c) (c)
d) No Error

Hint: The question suggests that, we have to figure out if all the three sub parts of the question are correct or not. Let us analyse all the three sub parts to identify if there exists any error. Check for subject- verb agreement, punctuation and correct use of prepositions.

Complete step by step answer:
Let us discuss all the three options in detail to check if they have been correctly formed.

a) (a): He does not listen to: This subpart is correct as it is in simple present tense and refers to someone who does not obey someone.
b) (b): what I say: This sub part is correct as it is simply an object to the preposition ‘to’ in the previous sub part.
c) (c): although I am advising him for a long time: This part seems incorrect as it refers to the verb advising that means giving suggestions for quite some time. Here, ‘for’ should be replaced by ‘since’ as the former represents purpose and the latter represents time. Also, it can be rewritten as ‘’although I have been advising him since a long time’’, ‘have been’ can be used as the verb; the sub part suggests that someone has been advising someone over a period of time. Therefore present continuous form can be used here.
d) (d): No Error: This option is insignificant as the error lies on the sub part c.

Hence, the correct answer is option c.

Note:
Analyse the prepositions, verbs, adjectives, nouns etc carefully and establish the right connection between them. If our subject is singular then we need to use the corresponding singular form of the verb. Same applies to plural. For instance: He study (incorrect); He studies(correct).