鸡蛋产出后,胚胎发育暂时停止,要使胚胎发育继续进行,必须提供的环境条件是( )
——Hello, this is Jack. Mary I speak to Tom?——Sorry, he isn't in at the moment. If he back, I'II ask him to call you back.
用反证法证明“三角形中最多只有一个内角为钝角”,下列假设中正确的是( )