Hello everyone,

I'm having problems with this exercise:

"I don't think I could / might have done what Mother Teresa did - she was a brave person."

I can't understand why COULD is the correct option. For me both are possible. In fact, according to a previous explanation (and the grammar reference) COULD and MIGHT can be used interchangeably:

"Look at this photo I took - I think I might be able to sell it to the newspapers."
"I suppose the reports could be true, but I doubt it."
It's possible that it's true.

"He's not in the office. He might have finished work early."
"She could have been at the party, but I didn't see her."
We talk about the possibility that past events happened.

Could anyone shed some light on this?