-          is your lemon juice? - It's sour.

①写出甲烷燃烧的化学方程式：____．

②沼气中除含有甲烷外，还含有二氧化碳及少量的氢气、氮气、硫化氢、一氧化碳、水蒸气等．沼气略带臭味，你认为臭味可能来自____气体．平时在我们家用的液化石油气中也加入少量带臭味的气体，其目的是____．

根据句意，用括号内单词的适当形式填空
（1）Stop ____  (make) so much noise. My father is sleeping .
（2） When I have an exam, I feel____  (worry) .
（3） Cathy ____ (go) to school on her bike yesterday.
（4）Bicycle is another way of____ (say) bike.
（5）You needn't____  (finish) your homework today. You can di it tomorrow.
（6） Do you know where Mike____  (live) ?
（7） A number of students in our school ____ (be) from the countryside.
（8） I take a taxi to work when it____  (rain).
（9） There are a few____  (different) between the two pictures.
（10） They often go bike____  (ride) on weekends .