Friends are angels(天使) to make us rise when our wings(翅膀) ha

Friends are angels(天使) to make us rise when our wings(翅膀) have problems flying.
这里不是运用到have sth.的语法点,而是have problems/trouble (in) doing sth. 做……有困难
介词in 可以省略,也可以用些词来修饰problems/trouble,例如 have much/ little/ no trouble (in) doing sth.
As I was walking, I saw a group of kids running toward him, knocking all his books out of his arms.
knock out of 把……从……里面敲出来,敲下来
knock意思是敲, out of是从……里弄出来
不能换成keeping out of
因为keep out of是躲开,置身…之外
跟这里要表达的句意不一样了~~

这个是固定搭配 have problems (in) doing sth. 介词in经常被省掉。
knock out of 碰出去，撞出去， 不能换