在下列各句的空格内填上一个适当的完整的单词，该词的首字母已给。
小题1:In autumn the leaves of most trees turn y________.
小题2:There’s no b________ over the river. We have to cross it by boat.
小题3:It’s best to water plants either e________ in the morning or late at night.
小题4:Many children like spending much money in b________ beautiful pencil boxes.
小题5:Before you come into the room, please k ________ at the door.

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