Answer:
Step-by-step explanation:
1. The strange man's reason for being there was difficult to ascertain.
The definition of ascertain is to find something out for certain or make sure of. I believe the word that would fit this sentence the best would be understand.
2. The teacher tried to facilitate discussion by asking questions.
The definition of facilitate is to make an action or process easy/easier, thus the phrase that fits this sentence best is Make easier.
3. It was necessary to employ a pair of pliers to pull back the metal.
A definition of employ is to make use of, and the word use would fit this sentence best.
I hope this helps :)