我总是学不好理科。

I was always weak in the science subjects.

不费力气什么都学不好。

You can't learn anything without making an effort.

你要是没有恒心可学不好。

Unless you persevere with a subject; you can't hope to master it.

然而很多美国人似乎都学不好它。

Yet many Americans seem to have a problem with it.

抄答案外加抄过程可学不好数学。

Copy copy answer process can be applied not learn mathematics.

贪图舒服和享受学不好英语的。

Seeking for comforts and enjoyment cannot give you good english.

英语太难，我学不好。（具体指出谁学不好）

English is too difficult for me to learn well.

没有足够的实践，外语是学不好的。

No one can learn a foreign language well without enough practice.

我担心我的数学怎麽也学不好。

I'm afraid I'm quite hopeless at mathematics.