有甲、乙、丙三种货物，若购甲3件，乙7件，丙1件，共需315元；若购甲4件，乙10件，丙1件，共需420元．现在购买甲、乙、丙各1件，共需（　　）

下面诗句朗读不正确的一项是（    ）

关于我国夏季气温的叙述正确的是（    ）

根据短文内容，选择正确答案。
Hello, friends!
    My name is Zhou Dan. I'm a Chinese girl. I'm twelve. I'm from Zhengzhou, China. Do you know Zhengzhou? It's in the middle of China. I'm in No. 8 Middle School. There are about 900 students and 50 teachers in our school. It is a good school in Zhengzhou: I'm in Class 2 Grade 7. There are 49 students in our class: 29 girls and 20 boys. My English teacher is Miss Zhao Dan. Our names are almost the same, right? She is nice to me. We're good friends. I like English, and I like music, too. I want to find a pen-friend. Please write to me.
                                                              Yours,
                                                            Zhou Dan

成语“金蝉脱壳”中，壳指的是（　　）