用括号里的单词的适当形式填空。

1. How much______these pants? They are fifteen dollars. (be)

2. I'm sorry I can't remember the length of the desk. Can you tell me how______ it is? (length)

3. Can I ______ you? Yes, please. I want a T-shirt.(helpful)

4. Cindy______a new blue sweater.(have)

5. Look! The red shoes are on ______for ＄15. (sell)

标准状况下6.72L烃在足量的氧气中完全燃烧．若将产物通入足量澄清石灰水中，得到白色沉淀质量为60.0g；若用足量的碱石灰吸收燃烧产物，碱石灰增重42.6g．

（1）计算燃烧产物中水的质量．

（2）通过计算推断烃的分子式．

（3）写出一种和该烃具有相同碳原子和氢原子数的烃的含氧衍生物的结构简式．