A: I find Tom is a little slow in the uptake.
B: Why do you say that?
A: I have explained the same question several times, but he just couldn't understand.
slow in the uptake：理解得慢，反應慢，領會得慢
e.g. I must be slow in the uptake: country folk's brains don't work as fast as yours.
e.g. Robert is so slow in the uptake because you have to tell him everything ten times before he gets it right.