571 suppose, supposing and what if
(...) A past tense makes the suggestion sound less definite.
Daddy, can I watch TV? ~ Suppose you did your homework first.
M. Swan, Practical English Usage, §571
I wonder what the daddy's reply means.
a) "I guess you've already finished your homework",
b) "I think you'll finish your homework first (if so,/so/then you can)",
c) "If you finish your homework first"
d) It's vague, and is more or less meaning all of the above.
Is it a kind of words that is typical from a parent to the kid?
Is there an omitted subject 'I' before the 'suppose'?