There were some trees before．Now there is a dining hall．
以下热现象的解释中正确的是（ ）
- Lucy, what were you doing at nine last night?
- I ___________ the piano. I usually practice the piano at that time.
秋日，树叶纷纷落下枝头，其中有一片梧桐叶从高为5m的枝头自静止落至地面，所用时间可能是（ ）
我国许多传统食品的制作都要利用细菌和真菌，下列应用中错误的是（ ）
