I _______ singing. （ ）
A：am
B：are
C：is
下图示意常见生活用品——袜子的生产流程。读图，回答下列问题。
“羌笛何须怨杨柳，春风不度玉门关”描述的是（ ）
(____) Is it on your desk?
(____) Sure.
(____) Excuse me! Can I use your eraser?
(____) Where is my eraser?
(____) Look! It's under the chair.
(____) No, it isn't.
