Read the passage carefully, then choose the correct option (marked A, B, C or D) to answer the questions.

Scientists have established that influenza viruses taken from man can cause disease in animals. In addition, man can catch the disease from animals. In fact, a greater numbers of wild birds seem to carry the virus without showing any evidences of illness. Some scientists conclude that a large family of influenza virus may have evolved in the bird kingdom, a group that has been on earth 100 million years and is able to carry the virus without contracting the disease. There is even convincing evidence to show that virus strain are transmitted from place to place and from continent to continent by migrating birds.

          It is known that two influenza viruses can recombine when both are present in an animal at the same time. The result of such recombination is a great variety of strains containing different H and N spikes. This raises the possibility that a human influenza virus can recombine with an influenza virus from a lower animal to produce an entirely new spike. Research is underway to determine if that is the way major new strains come into being. Another possibility is that two animal influenza strains may recombine in a pig, for example, to produce a new strain which is transmitted to man.

According to the passage, scientists have discovered that influenza viruses______.

KEEPING YOUR DISTANCE

Three hundred and fifty years before the first men looked down on the amazingly beautiful surface of the moon from close quarters, Galileo’s newly built telescope (1)_______ him to look at the edge of the hitherto mysterious sphere. He saw that the apparently (2)_______ surface was not divinely smooth and round, but bumpy and imperfect. He realized that although the moon might appear (3)_____, resembling a still life painted by the hand of a cosmic (4)_____, it was a real world, perhaps not very different from our own. This amounted to a great (5)______ hardly to be expected in his day and age, although nowadays his (6)______ may appear to some to be trivial and (7)________.

       Not long after Galileo lunar’s observations, the skies which had previously been so (8)________ revealed more of their extraordinary mysteries. Casting around for further wonders, Galileo focused his lens on the (9)_______ planet of Jupiter. Nestling next to it, he saw four little points of light circling the distant planet. Our moon it appeared, perhaps (10)_______ in the eyes of those fearful of what the discovery might mean, was not alone!

Several hundred million years ago, plants similar to modern ferns covered vast stretches of the land. Some were as large as trees, with giant fronds bunched at the top of trunks as straight as pillars. Others were the size of bushes and formed thickets of undergrowth. Still others lived in the shade of giant club mosses and horsetails along the edges of swampy lagoons where giant amphibians swam.

          A great number of these plants were true ferns, reproducing themselves without fruits or seeds. Others had only the appearance of ferns. Their leaves had organs of sexual reproduction and produced seeds. Although their “flowers” did not have corollas, these false ferns (today completely extinct) ushered in the era of flowering plants. Traces of these floras of the earliest times have been preserved in the form of fossils. Such traces are most commonly found in shale and sandstone rocks wedged between coal beds.

          Today only tropical forests bear living proof of the ancient greatness of ferns. The species that grow there are no longer those of the Carboniferous period, but their variety and vast numbers, and the great size of some, remind us of the time when ferns ruled the plant kingdom.