Could vs Could have p.p

"We did what we could have done" doesn't sound right. The other one is OK, but the usual way of saying this is probably "We did what we could".

What about this example:
e.g
' i used a nonsense word to make sure that the children might not be influenced by the things they had learned before'

' i used a nonsense word to make sure that the children might not have been influenced by the things they had learned before'

bmojtabaWhat about this example:e.g' i used a nonsense word to make sure that the children might not be influenced by the things they had learned before'' i used a nonsense word to make sure that the children might not have been influenced by the things they had learned before'

The combination "make sure ... might" does not work properly. It seems that you mea

GPYThe combination "make sure ... might" does not work properly.

Basically by using ' Might not be influenced' I wanted to clarify the degrees of certainty, because the probability of my statement was not 100%, if it was i would be saying ' would not be influenced' , am i correct?

bmojtabaBasically by using ' Might not be influenced' I wanted to clarify the degrees of certainty, because the probability of my statement was not 100%, if it was i would be saying ' would not be influenced' , am i correct?

"make sure" itself has a fairly high degree of certainty. To express uncertainty you could say "try to make sure that the children were n