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

Behind the eight ball

Better half．

Big wig

Bite one's lip

Bite the bullet

Black sheep

Blessing in disguise

Bom yesterday

Break a leg

Bum the midnight oil

Bury head in the sand

Butter up

Catch some Zs

Catch-22

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