to build up: to increase slowly, to make stronger gradually Examples of TO BUILD UP They certainly have built up a vibrant user community in a short period of time. These deficits have been built up over the past 10 years and nobody said a peep.  

to make friends: to become friendly with others Examples of MAKE FRIENDS Once you’re done with college, it’s hard to make friends, but it isn’t impossible. The kittens approached each other tentatively, hoping to make friends.  

to brush up on: to review something in order to refresh one’s memory Examples of TO BRUSH UP ON The old doctor mistakenly thought he didn’t need to brush up on the procedure, and it caused more complications for the patient. Let’s brush up on our sales techniques before the holiday rush.

to blow up: to inflate, to fill with air; to explode, to destroy (or be destroyed) by explosion Examples of TO BLOW UP Linda must have been pretty angry to blow up at you like that. A storm blew up off the east coast.

to be in charge of: to manage, to have responsibility for Examples of TO BE IN CHARGE OF I can’t wait to be in charge of a big corporation. Veronica was in charge of handling scheduling while Frank’s regular secretary was on leave.

to take hold of: to grasp, to grip with the heads Examples of TO TAKE HOLD OF The police needs to take hold of the situation before it goes out of control. We were able to take hold of the throttle and stop the runaway train.