in reservor two tube leaks, the first tube can fill an empty bucket in x hours, and the second tube alone can fill the same bucket in y hours, where x<y, if both tubes began leaking at the same time into the empty bucket at their respective constant rates and consequently it took t hours to fill the bucket, which of the following must be true?
I 0<t<y
II x<t<y
III x/2<t<y/2

I only
II only
III only
I and II only
I and III only