读一读，选择正确的单词补全句子。
【小题1】I have _________ (second / two) pens.
【小题2】Can I have __________ (a / an) apple, please?
【小题3】My classroom is on the ___________ (first / one) floor.
【小题4】How many __________ (ruler / rulers) do you have?
【小题5】Let us clean the __________ (teacher's / teachers') office.