I know you---(choose)a picturebok among these.

知道(know)是现在,而选择(choose)是过去了,从过去发生的动作对现在有影响或结果就要用现在完成时.
如果是此句就可以用两种时态都对,You choose a picturebook among these.或You chose a picturebook among these.因为没具体的上下文.