婴儿在母亲体内发育九个月。

The baby ___develops inside the mother for nine months.

随着时间的推移，他们的相识发展成了一段持久的友谊。

Over time, their acquaintance ___developed into a lasting friendship.

这项运动旨在发展肩部和背部肌肉。

This exercise is designed to ___develop the shoulder and back muscles.