.At the meeting they discussed different ______ to the study of mathematics.
I’ve kept up a friendship with a girl whom I was at school ________ twenty years ago.
In the experiment we kept a watchful eye ________ the developments and recorded every detail.
I don’t think it’s fair to judge a person ________ their clothes.
I am anxious about what notes he made in the back of his diary ________ things to mend or replace.
The customer bargained with the shopkeeper for a long time, and finally they agreed ________ the price.