Read each sentence to find out whether there is any grammatical error in it. The error, if any will be in one part of the sentence. The letter of that part is the answer. If there is no error, the answer is 'E'. (Ignore the errors of punctuation, if any).
They could have helped him, had they approached by him for help well in advance.
They could have
helped him,
had they approached by him
for help well in advance.
No error
Correct answer is C
had they been approached by him