“You can’t have this football back ______ you promise not to kick it at my cat again.” the old man said firmly.

问题描述:

“You can’t have this football back ______ you promise not to kick it at my cat again.” the old man said firmly.
选项:
a、because
b、 since
c、 when
d、 unless

d
我不能把足球还给你,除非你承诺不再用它踢我的猫.