Read the sentence 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 corresponding letter of that part is the answer. If the given sentence is correct as it is, then choose option ‘No error’ as the answer response. (Ignore errors of punctuation, if any).

After attending the workshop(A)/ on digital marketing, she learn (B)/valuable strategies to (C)/enhance her online business (D).

Correct option is B

The error lies in part (B).
The error in the sentence is in the part (B). The verb "learn" should be in the past participle form which is "learned".
The error in the sentence is a verb tense inconsistency. The verb "learn" in part (B) of the sentence is in the present tense ("learn"), but the sentence is describing a past action because it mentions that she attended the workshop in the past ("After attending the workshop").
Here's the corrected sentence:
"After attending the workshop on digital marketing, she learned valuable strategies to enhance her online business."