区分海相与陆相地层的重要相标志通常是（）、（）和（）。
参考答案：综合标志；生物标志；化学标志
–Mr Green, can we do to protect ourselves when facing dangerous attackers in public places?
–Always remember “run, hide and fight” when you are in danger.
A．what
B．how
C．where
D．which
