ask for help后面加什么介词

Learn to ask for help when needed.

学会在需要的时候寻求帮助。

Only ask for help when you need it.

只在需要帮助的时候才去寻求帮助。

Whom did the baby snail ask for help, his mother or father?

小蜗牛向谁求助了，他的妈妈还是爸爸？