Naturally, m a group of animals as diverse as thesnakes, and with so many varied enemies. there arenumerous defensive reactions and devices. Thereis. however, one general pattern of behavior. In thepresence of suspected enemy the first reaction isto try to escape observation; if this fails, the nextresort is the flight co some inaccessible retreat, but if this is not possible, or iscircumvented. various kinds of intimidatory gestures and warning devices are brought

　　into play; in the last resort the snake attacks. This pattern vanes with the circumstances; some stages may be omitted or combined unpredictably whilst all some notoriously irasciblespecies may dispense with all the preliminaries and attack almost at once. though seldom ornever without some provocation.

　　Amongst the factors that increase aggressiveness are hunger, the mating season and surprise, with the last mentioned the commonest; when hunting for food or for mate. activity and theaggressive instinct are both at their peak. Owing to their poor sense of hearing snakes arevery liable to be, quite literally, caught napping and a similar situation arises during theirperiods of temporary blindness just before sloughing (蜕皮)begins. By far the greatestnumber of snake-bit accidents result from the unwitting disturbance of resting snakes. and thishazard is much increased with species that are well disguised and whose natural instinct is totrust to this concealment as their principal defense. As well as differences in aggressivenessbetween individuals of the same species according to the circumstances and conditions, thereare also notable differences between species, even closely allied species; and the reports ofthose who have been attacked may understandably be lacking in objectivity. So it isimpossible to forecast. even in outline, how any encounter will develop.

　　The Hamadryad, for example, is usually credited with being amongst the most aggressive ofsnakes. and there are many accounts of unprovoked attacks, yet on one occasion fourteenmen and seven dogs passed and returned within two yards from a nest and no snake was seenalthough the female. which guards the nest, could not have been far away.

　　1.When a snake meets a potential enemy, itsprimary device is______________.

　　A) avoiding any observation

　　B) Finding a safe shelter

　　C) giving a warning threat

　　D) starting a quick attack

　　2.The underlined phrase "dispense with all the preliminaries" in Paragraph I mostprobably means________________.

　　A) the snakes combine all the previous three steps

　　B) the snakes give up all the previous three steps

　　C) che snakes follow all the previous steps one by one

　　D) the snakes reverse the order of all the previous steps

　　3.A snake is most aggressive when_______________.

　　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 che mating season

　　4.It is difficult to predict what would happen when a snake meets a manbecause____________.

　　A) no one bas ever clearly known how he himself was bit

　　B) man tends to be subjective when he describes his encounter with a snake

　　C) the aggressiveness of the snakes differs according to diverse situations

　　D) a snake does not begin co attack without provocation

　　5. The author uses the example in the last paragraph m support his ideathat___________.

　　A) snakes do not begin the aggressive act if it is not disturbed

　　B) some snakes are more aggressive and more ready to attack

　　C) it is hard to forecast whether and how snakes would attack

　　D) snakes often conceal themselves as their principal defense