请根据句意及汉语提示，写出所缺单词。
________ (叶子) will turn green when spring comes.
I ________ (想知道) why he is late for school again.
I wrote a letter to him two days ago, but he didn’t ________ (回复) to me.
He often ________ (跟随) me up the hill.
—Do they like eating ________ (三明治)?
—No, they don’t.