A．the snakes combine all the previous three steps.
B．the snakes give up all the previous three steps.
C．the snakes follow all the previous steps one by one.
D．the snakes reverse the order of all the previous steps.

A．it meets a possible enemy.
B．it is caught when it is sleeping or sloughing.
C．it is disturbed unknowingly.
D．it seeks a partner in the mating season.

A．no one has ever clearly known how he himself was bit.
B．man tends to be subjective when he describes his encouhter with a snake.
C．the aggressiveness of the snakes diversify according to different situations.
D．a snake does not begin to attack without provocation.