89.A three-year-old might need help in understanding that other children feel pain just as he does, and that hitting a playmate over the head with a heavy toy requires an apology.

　　主干：A three-year-old might need help

　　解析：in understanding... 是介詞短語作狀語，表示在明白...方面。understanding后面有兩個that 引導的賓語從句。前一個從句中，as he does 引導的是比較狀語從句，修飾feel pain。后一個從句中，hitting...是動名詞作主語，謂語動詞requires用單數(shù)形式。