单选题The boss believed Tom's&n

问题补充：

单选题ThebossbelievedTomsreasonforbeinglateforworkis______hehadtohelphisgrandmacook.A.whyB.thatC.whereD.because he

答案：

B解析考查表语从句。That he had to help his grandma cook是一个表语从句，这个句中结构很完整，that只起引导作用，不充当任何成分。