can tell
I could tell she was really nervous.
:__________________。
It's often hard [difficult] to tell whether a child is ill.
:子供が病気かどうかを__するのは難しいことが多い。
There's no telling how deep it is. = It's impossible to tell how ...
:彼が何を考えているのか_______ときがある。
I could tell _ [__] looking at you what happened.
:君を見て何が起こったかわかった。
He could not tell the difference between one flower and another.
:彼は花の違いを____ことができなかった。
Optimized studying based on the forgetting curve vastly improves memorization. - What is reminDO?
Memorize