Do you know why I can't drink a whole can/glass of coke at once?
Can you guess why I can't finish a whole can of coke in one gulp?
ーDo you know why I can't drink a whole can/glass of coke at once?
「なんでコーラの一気飲みができないか知ってる?」
drink a whole can/glass of coke で「一缶/一杯のコーラを全部飲む」
at once「一度に・一気に」
ーCan you guess why I can't finish a whole can of coke in one gulp?
「なんでコーラの一気飲みができないか分かる?」
finish a whole can of coke で「一缶のコーラ全部を飲み干す」
in one gulp「ゴクリと・一気に」
ご参考まで!