A diamond in the rough
A drop in the bucket
A frog in one’s throat
A piece of cake
A shot in the dark
Achilles’ heel
An arm and a leg
An eye for an eye
Apple of your eye
Armed to the teeth
As cool as a cucumber
At the drop the a hat
At the eleventh hour
Back to square one
Backseat driver
Ballpark figure
Ball's in your court
Beat around the bush
……
