It’s a teacher’s _____ to make children learn.

We could not reason out the way the robbers escaped，because we were unable to find any ________ of them.

The great _______ of my plan is that it’s so cheap compared to the others.

At last, I should thank Mr. White for the _______ of speaking here and for ensuring me such an attentive audience. 

On your way to New York William will keep you ______if you don't want to be lonely.