—You know. Bob is a little slow ____ understanding, so…— So I have to be patient ______ him. 

The boss insisted that every minute ______ made full use of ______ the work well.

–There is _______ on using mobile phones at the gas station. --Do you mean talking on the mobile phone ________ at the gas station?

They use computers to keep the traffic _______ smoothly. 

Although ______ for many years, the two old sisters recognized each other at once.