已知：3Cu+8HNO₃=3Cu（NO₃）₂+2NO↑+4H₂O，现把19.2g Cu放入足量的稀硝酸中，微热至Cu完全反应．求：

与现在的大气组成相比，原始大气中缺少的最重要的气体是____．

从右栏中选出与左栏相应的答句。

①Is this your school?____                                                            A.There are three.

②How is your brother, Tom?____                                                B.I'm a student.

③Is there an art room in your school?____                                 C. She's Jack's sister.

④What are you?____                                                                    D. Yes, it is.

⑤How old is he?____                                                                    E. No, there aren't.

⑥Is Mrs. Li a teacher?____                                                            F. Thank you very much.

⑦Are there five boxes on the desk?____                                    G. He's fine.

⑧How many rubbers are there in th edesk?____                       H. Yes, there is.

⑨Sit down, please.____                                                                I. No, she isn't.

⑩Who's she?____                                                                       J. He's twelve.