You       find it so hard to write the composition now if you had observed life carefully

A．wouldn't

B．didn't

C．don't

D．mustn't

已知下列元素的原子半径：

A．0.80×10^{10 m                                            B}．1.10×10^{10 m}

C．1.20×10^{10 m                                            D}．0.70×10^{10 m}