Heisveryhumorous,whilehisbrotherisratherserious.Thatis...

問題詳情：

 He is very humorous, while his brother is rather serious. That is ＿＿ their difference lies.

A. why              B. where          C. how            D. when

【回答】

AAC

知識點：連詞

題型：選擇題