English grammar error-spotting (verb + preposition: ‘‘enquire of/ask (someone)’’): ‘‘He enquired me / why I had not seen him the previous day / as I had promised to do. / No error.’’ Pick the erroneous part.

Concept / Approach
In formal English, ‘‘enquire’’ is used with a preposition (‘‘enquire of someone’’) or with ‘‘about/into’’ something; or we use ‘‘ask’’ with a direct object (‘‘asked me’’).

Correction
‘‘He asked me why I had not seen him the previous day …’’ or ‘‘He enquired of me why …’’

Why B & C are fine
‘‘the previous day’’ correctly backshifts time in reported speech; ‘‘as I had promised to do’’ is grammatical and idiomatic.

Final Answer
He enquired me