根据下列句子及所给单词的首字母，用适当形式填空。（每空限填一词）
People should stop cutting down trees, or the e         will become worse.
My mother is cooking in the kitchen. I think she is a great c       .
There are h           of birds in the sky.
Mr. Wang looks s        . He is always strict with us.
My sister was not happy, because she l       her favorite toy yesterday.