take sth into account	consider sth
on account of	because of
on no account	under no circumstances
on this account	for this reason
on the air	broadcasting
off the air	not being broadcasted
up in the air	it exists but not talked about
clear the air	remove suspicion or bad feeling
be up in arms	be very angry
on the alert	expecting sth
act on	do whatever is advised
act up	behave awkwardly or not work properly
answer sb back	respond rudely to sb
answer for	be responsible for sth
answer to	be under the command of sb
back down	cease to oppose or demand
back out (of)	withdraw from
back up	support/confirm
bear on	be relevant to
bear with	be patient