如果不及时修理，这座桥会慢慢老化损坏。

If not repaired in time, the bridge will gradually ___decay.

水果放在桌上太久会腐烂变质。

Fruits left on the table too long will start to ___decay.

铀原子会自然衰变成其他元素。

Uranium atoms naturally ___decay into other elements.