The following sentence has been divided into parts. One of them may contain an error. Select the part that contains the error from the given options. It is imperative in understanding / the rising importance of artificial intelligence / in the public sector to increase the efficacy / and impact of the work done for public welfare.

Find the part of the sentence that contains a grammatical error: (1) Scarcely had the newly appointed Director of Intelligence assumed her post / (2) when a sophisticated cyber-espionage campaign was detected / (3) within the high-security servers of the national defense agency, / (4) prompted an immediate and total lockdown of all external communication channels.

Find out which part of the following sentence contains a grammatical/contextual error: I congratulate you (A)/ on your success (B)/ in the examination (C)/ that never happened last week (D)