下列各式中成立的一项 （ ） A． B． C． D．
下列正方体或正四面体中，P、Q、R、S分别是所在棱的中点，这四个点不共面的一个图是
Men have always believed that they are smarter than women. Now, a study has found that while this is certainly true, men also have to deal with the fact that they are also more stupid than the fairer
用大豆新鲜绿叶进行如图装置的实验，置于充足的光照下，分析D处的气体成分，最可能发现( ) A．O2量多于B处 B．O2量与B处一样多 C．无CO2和O2 D
关于运动的性质，以下说法中正确的是（ ）A．曲线运动一定是变速运动B．变速运动一定是曲线运动C．曲线运动一定是变加速运动D．物体加速
B Energy-saving Finns invented the first ice skate more than 5,000 years ago, as a practical method of transport to make getting across frozen lakes less of a struggle. The earliest skates would have
有关密码子的叙述，正确的是 ①一种氨基酸可能有多种与之对应的密码子②密码子GCA在人细胞与细菌细胞中决定的氨基酸相同③GTA、CCC、AUG都是密码子
在口中咀嚼米饭和馒头时会感到有甜味，这是因为 ，它能将食物中部分淀粉催化水解为麦芽糖的缘故。
