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).
Reasonable ambition, if supported at persistent efforts, is likely to yield the desired results.
Reasonable ambition, if supported
at persistent efforts,
is likely to yield
the desired results.
No error
Correct answer is B
by persistent efforts