现在进行时构成 — 英语词汇题
题目
用所给动词的适当形式填空，注意主语与时态标志词：1. Listen! The girl ______ (sing) an English song in the classroom. 2. Tom and his sister ______ (not do) their homework now; they ______ (watch) TV. 3. — ______ you ______ (write) a letter? — Yes, I am.