Explanation

Before the workshop, the writers’ comments were general and unhelpful; the time triggers in the sentence tell you that things were different after finishing the editing workshop, so you need a word like specific or helpful in the blank. Three of the choices—cursory, superficial, and amateurish—are nearly the opposite of what you’re looking for, so eliminate choices (A), (C), and (D).

Derisive, which means scornful, isn’t supported by the sentence, so eliminate choice (B). Both critical and constructive can describe comments that are specific and helpful, so choices (E) and (F) give you appropriate, equivalent sentences.

Hence options E and F is correct!