Read the sentence given below to find out if it contains any error. The error, if any, will be in one part of the sentence. If the sentence is error free, select No error or option 5. Ignore error of punctuation if any.

The 2020s must be the decade when (A)/ the world changes course, before (B)/ the level of carbon in the atmosphere rises too high (C)/ to avoid dangerously levels of heating. (D)/ No error (E)