阅读理解                                                           

                                                                Table manners in America

        Don't circle your plate with your arms. If you do so, you will become the focus  (焦点)  of the table. Everyone would wonder, "Is there anything wrong with the food?" This may give a wrong message that you don't like the food or something like that.

       Don't push the plate back when finished. Leave it where it was. Do you want to let the hostess (女主人)(1)_________(know ) that you've just done a labours。

        Don't lean (倚靠) back and say "I'm through" or "I'm full". Just put the fork and knife across the plate. That's all. 

       (2)Don't cut up everything before you start to eat. Cut only one or two bites (块) at a time. Never take a huge mouthful of anything. Do you want to show how hungry you are? Don't do that. It's not so good.

        It's never good to reach across the table for anything. If the thing you want is not at hand, simply ask the nearest person for help, like "(3) Mrs. Smith, could you pass me the dish?"

下列哪一类植物有茎和叶的分化，但没有输导组织（　　）

地沟油中含有一种强烈致癌物黄曲霉素B₂（C₁₇H₁₄O₆），长期食用会引起消化道癌变，请回答：
(1)黄曲霉素B₂中元素的原子个数比为____；
(2)15.7g黄曲霉素B₂中含有____g氧元素。