下面是四位同学学完《原子核的组成》这节内容后，对这节内容的认识，你认为错误的是（ ）
A．原子的种类大于元素的种类
B．原子质量主要集中在原子核
C．所有的原子都含有质子、中子和电子
D．12C与14C互为同位素
A．元素是具有相同核电荷数的一类原子的总称，有的元素可能有多种同位素，所以导致原子的种类大于元素的种类，故A正确．
B．原子是由原子核和核外电子构成的，核外电子的质量很小，约是质子质量的
，可忽略不计，所以原子的质量主要集中在原子核上，故B正确．1 1836
C．11H没有中子，故C错误．
D．12C和14C是同一元素的不同核素，互称同位素，故D正确．
故选C．
| 完形填空。 | |||
| I stood in the doorway, watching my older brother carefully putting clothes into his bag. I coughed uneasily. Finally __1__ that I was there, Rocky turned toward me with a sad smile. "I'm __2__ tomorrow," he said. "I know." My __3__ was almost a whisper (低声). I was __4__ at myself for being so weak ,but I wasn't about to cry . "My 20 is early ,so there is still __5__ time to come to the airport," he said .Seeing the __6__ look on my face , he quickly added, "I promise (答应) I won't leave without saying goodbye." I tried to say __7__ , but didn't . It's always __8__ to keep quiet if you're about to cry . "You promised you wouldn't cry," he said to me, thinking that I was close to __9__ . I remember the day he taught me how to ride a bike. __10__ I thought he was always right behind me, holding the seat to keep me from __11__ . I was happy with this, but he knew he couldn't hold me up all my life . He told me that one day he would have to let go. His coughing stopped my thinking .What was left to say? How could I say __12__ to the person who taught me everything? The next morning I __13__ , looked at my alarm clock , and realized he had left __14__ ago .We never even said goodbye. Goodbye, Rocky! Although he may have been many miles away, I knew he heard me, even if it was only an answer in his heart. | |||
| ( ) 1．A．forgetting ( ) 2．A．arriving ( ) 3．A．voice ( ) 4．A．glad ( ) 5．A．ship ( ) 6．A．enough ( ) 7．A．surprised ( ) 8．A．anything ( ) 9．A．stranger ( ) 10．A．tears ( ) 11．A．At last ( ) 12．A．riding ( ) 13．A．goodbye ( ) 14．A．gave up ( ) 15．A．minutes | B．realizing B．living B．sound B．moved B．flight B．little B．excited B．everything B．better B．smiles B．From now on B．running B．hello B．stood up B．hours | C．watching C．coming C．noise C．angry C．train C．no C．sad C．something C．worse C．words C．At first C．walking C．yes C．looked up C．days | D．learning D．leaving D．word D．pleased D．bus D．busy D．happy D．nothing D．easier D．sadness D．So far D．falling D．sorry D．woke up D．weeks |