Because "B" shells are to small and "D" shells are too big.
Ehh, it depends.
Joke: Why don't birds have to wear camouflage? Punch: Because they are already "in the skies". Thank you, I'll see myself out.
Gotta lay off the sea-weed.
Her algae bra.
Because "B" shells would be too small!
Cause the B-shells were too small.
Because B-shells are too small and D-shells are too big!