The claims of students look hollow when they attribute their poor performance to difficulty of examination.

Answer: Option C

Inundate : overwhelm (someone) with things or people to be dealt with.
Inhere : exist essentially or permanently in.
Impute : represent (something, especially something undesirable) as being done or possessed by someone; attribute.
Infer : deduce or conclude (something) from evidence and reasoning rather than from explicit statements.
Attribute : regard something as being caused by.

Synonym of Attribute is Impute