云海壮观、擎天神木、日出奇景、艳红樱花是______最著名的四大自然名景。
参考答案：阿里山
You________ the work better, but you didn’t put more efforts to it.
A．must have done
B．can have done
C．should have
D．could have done
（）原料所产生的沼气中硫化氢含量高。
A、猪粪
B、鸡粪
C、牛粪
D、秸杆
