哥哥没准备好考试，把‘了’去掉。

我吃完了一个苹果。我吃掉了一个苹果。不用”好“，

我听完了你的话，但是我没听懂。 我听你说完了，但是我没听懂。

1:correct

2:delete 了 

3:actually 吃好了also means吃完了,but we always use 吃好了 when we are refering to finish meals instead of eating apples.

4:个means a, an or one, but we can't use 个 separately，you must put a number before个.E.G     一个，两个，三个                                                                            and you can't put two 个 together,there is no things as such.

5:说can only be used as a verb,you can choose either 话 or 说话 to use as nouns,but not 说for example

what did you say说

i heard what you said(你的话 or 你的说话)