do (your) homework

to learn everything you need to know before doing something.

If you had done your homework, you would have known it was a silly question to ask.

• diamond in the rough
• dibs on
• dibs on something
• dice are loaded against
• dice are loaded against someone
• dice with death
• diddly-squat
• die a death
• die down
• die for
• die-hard
• die hard
• die is cast
• die off
• die out
• die with boots on
• die with your boots on
• difference of opinion
• different ball of wax
• different strokes
• different strokes for different folks
• different strokes for different folks.
• dig deep
• dig heels in
• dig in