Directions: Read the sentence carefully to find out whether there is any grammatical or idiomatic error in it. The error, if any, will be in one part of the sentence. The number of that part is the answer. If there is no error, mark D. (Ignore the errors of punctuation, if any.)

(A) Mother told me that (B) I could have achieved success (C) if I had not wasted my time and energy on trifling matters. (D) No Error

This is a conditional statement. This kind of statement is used when we talk about something generally not expected to occur or is purely imaginary. Here, the mother says that I could have achieved success (this means I have not achieved success) if (this is the condition) I had not wasted my time and energy on trifling matters (means I have wasted my time and energy on trifling matters). The sentence is perfectly in order.