单句改错（共5小题; 每小题1分，满分5分）
此题要求改正所给句子中的错误，每句只有一处错误，必须按下列要求改正：
该行多一个词：把多余的词用斜线（\）划掉。
该行缺一个词：在缺词处加一个漏字符号（∧），在下面写出该加的词。
该行错一个词：在错的词下划一横线，在下面写出改正后的词。
小题1: Last night, his father came back late as usually.
小题2: At the end of 16^th century, about five to seven million people spoke English.
小题3:The Mekong River becomes rapids as it passes across deep valleys.
小题4:This is the reason why she explained to me just now.
小题5:The boss requested that all the work must be finished as soon as possible.