His mood alternates between joy and despair.

他時(shí)而快樂，時(shí)而絕望。

語言點(diǎn)：sb./sth. alternates between two things，意思就是they keep changing between them，在兩者間交替

這篇材料你能聽出多少？點(diǎn)擊這里做聽寫，提高外語水平>>