What’s the difference between 始まっている最中に and 始まろうとしているとき in this context?

Question

I am currently studying for the JLPT N2, and I am confused about the answer for this particular practice question:

会議が（　　　）リンさんが慌てて入ってきた。

I put 始まっている最中に as the answer, but my textbook tells me that the correct answer is 始まろうとしている。

My thought process behind this answer was that 最中に is usually followed by an act of interrupting the task at hand, and I interpreted this situation as リンさん interrupting the starting of the meeting.

Is there a specific reason to why 始まろうとしているとき is the correct answer?

I’m really confused because 始まっている最中に (in the middle of starting) and 始まろうとしているとき (when about to start) sound really similar to me.

Answer 1

始まっている最中 itself sounds strange. The verb 始まる refers to an instantaneous change of state, not a durable action. Therefore, 始まっている usually describes a state where something has already begun. 最中, on the other hand, requires an ongoing action.

始まろうとしているとき refers to a stage where something is about to begin.