She alternated singing and dancing.

她一会儿唱歌，一会儿跳舞。

Joy and grief alternated in my heart.

我心中悲喜交替。

Hope and fear alternated in my breast.

我忽而充满希望，忽而担心。

His parents alternated in looking after him.

他的父母轮流看护他。

He alternated between hope and despair.

他时而充满希望，时而绝望。