1·The city should seal off those tunnels.
这个城市应该封闭那些隧道。
2·MicroRNAs could be used to seal off human cells from disease-causing viruses, or to disable viruses that gain entry.
小分子核糖核酸可以用来封闭人体细胞,使之免受致病病毒的侵扰,或者使病毒丧失侵入细胞的能力。
3·But we shouldn't fall and seal off ourselves.
但是我们应该堕落,更不能自我封闭。