荷兰某机构计划2023年把志愿者送上火星,这个计划可行吗?志愿者飞往火星途中,会遇到的困难是( )
①宇宙空间强辐射 ②火星引力强大 ③火星大气层稠密 ④环境长期失重.
A:①③
B:②④
C:②③
D:①④
---Our teacher is always kind.
---Yes. When she asked me to answer her question yesterday, I gave a wrong answer at first. She _______me to try again.
下列有关生物体的体细胞不能无限长大的原因的叙述,错误的是( )
下列有关物质的检验方法和结论都合理的是( )