Question

       It’s impolite to spit out the first bite of your dinner. But to a type of Australian snake, this rude behavior is a matter of life and death.

       The snake, called a floodplain death adder(蝰蛇), eats two types of frogs that are hard to stomach. The frogs produce chemicals to defend them from predators（猎食者）.

       One of these species, the Dahl's frog, can kill a snake that tries to eat it. The other species, the marbled frog, is less dangerous but still tough to eat. When attacked, it produces a glue like substance. Leaves and branches get caught up in this material, making a big sticky mess that gets in the way of anything trying to swallow it. A marbled frog can even get stuck on the head of an attacking snake.

       Both frogs have good defense methods. But the floodplain death adder knows how to get around each of them.

       Floodplain death adders quickly strike these frogs, using their poisonous teeth to inject poison. But then, instead of swallowing their dinner immediately, the snakes sit back and wait for their preys to become safe to eat. That's because both the Dahl's frog's protective toxin(毒素) and the marbled frog's glue break down over time. After a while, the frog toxin is no longer poisonous and the glue is no longer sticky.

       The two substances break down at different rates, and floodplain death adders seem to know the difference, And adder waits for a different length of time depending on the species of frog it just struck.

       The stickiness of the marbled frog glue decreased by as much as two-thirds after just 10 minutes. And that's just about how long an adder waits before eating a marbled frog.

       On the other hand, the snakes wait for about 40 minutes before eating a Dahl's frog. That's enough time for the frog's toxin to break down into harmless substances.

       But even a quick strike gives a taste of the Dahl frog's toxin. After striking such a frog, a floodplain death adder thrashes(翻腾) around and lies on its back with its mouth open, It's like the snake has just had a mouthful of chili pepper.

      By comparison, when given frogs that have no chemical defenses, floodplain death adders eat their prey immediately after striking. Snakes, despite the fact that they’ve got this tiny pea-size  brain are clearly capable of recognizing what kind of frog they’ve bitten.

1．What’s the best title of the passage?

       A．A dangerous meal

       B．A snake——floodplain death adder

       C．Two types of frogs——Dahl’s Frog and Marbled Frog

       D．The method of killing frogs

2．The underlined word “it” in the 3^rd paragraph refers to the        .

       A．marbled frog                                       B．Dahl’s frog

       C．floodplain death adder                          D．glue

3．The glue produced by the marbled frog is used for               .

       A．sticking the snake’s head

       B．making a safe place to live in

       C．preventing anything from tying to attack it

       D．killing an attacking snake

4．From the passage we can conclude that           .

A．the Dahl’s frog carries enough poison to kill a snake but only if the snake eats it immediately

       B．the floodplain death adders only eat the Dahl’s frog and Marbled frog

       C．although the snakes have tiny pea – size brain , they are cleverer than human beings

       D．both the Dahl’s frog and the marbled frog protect themselves by producing toxin

5．What’s the floodplain death adder’s method to make the frogs safe to eat ?

       A．They thrash around with their mouths open

       B．They sit back and wait for their preys to become safe to eat

       C．They inject poison on the preys and wait for the breaking down of their toxin and glue before eating them

       D．They quickly strike these frogs

Answer 1

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