I. Read the following sentences and explain the use of modal verbs in them

1. These two central cell nuclei may become a binucleate cell, or the may fuse together, forming a single diploid nucleus.

2. Plants range in size and complexity from small, nonvascular mosses, which depend on direct contact with surface water, to giant sequoia trees, the largest living organisms, which can draw water and minerals through their vascular systems to elevations of more than 100 m.

3. The nucleus must not only synthesize the mRNA for many thousands of proteins, but it must also regulate the amounts synthesized and supplied to the cytoplasm.

4. On the one hand, water vapour is a greenhouse gas, and its increased presence should add to the insulating effect. On the other hand, more vapour in the atmosphere will produce more clouds, which reflect sunlight back into space, which should slow the warming process.

5. Gene therapy might help older people to regain strength in withered muscles and density in thinned bones, and to increase pumping power in their aging hearts.

6. One female silkworm moth need release only 10^-8 grams of sex attractant per second in order to attract every male silkworm moth in a volume hundreds of meters to kilometers on a side.

7. Some researchers predict that in the distant future gene therapy could be used to eliminate genetic defects from families or even to produce “designer babies” with more muscle strength, higher intelligence, sweeter dispositions, or whatever traits parents desire.

II. Fill in can, may, must, need, should, might, and could in the sentences below

1. Researchers approached the use of retroviruses with caution because of concerns that they _____ attack inappropriate cells.

2. Neither ATP nor ADP, being large, charged molecules, ___ cross the membrane unaided, but ADP ____ enter and ATP ____ leave the mitochondrial matrix in order for ATP synthesis to continue.

3. Conservatives have argued that too much public money is being spent on the environment and that the federal government ____ play a much-reduced role in environmental regulation.

4. Heterotrophs — organisms that ____not manufacture their own food — usually lead less sedentary lives than plants, but they ultimately depend on autotrophs as sources of food.

5. Auxin, one of the most important plant hormones, is produced by growing stem tips and transported to other areas where it ____ either promote growth or inhibit it.

6. Once gene therapy methods have been developed in a laboratory and tested on animals, scientists ____ to prove that they work in humans.

7. Many people feel that because gene therapies use altered genes and potentially dangerous viruses, these treatments ____ be more extensively tested than drugs before being approved.

8. The extraordinary potential of gene therapy has also raised alarms among critics who warn that the technology ____ go too far.

9. Germ-line therapy is highly controversial because genetic alternations made to germ cells would change the genetic endowment of the unborn and ____ be passed on to future generations.

10. Today many domesticated plants ____ scarcely be traced back to their wild ancestors or to the original plant communities in which they originated.

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VII. Use the words from the previous exercise in the following sentences	\|	III. Translate the following sentences using modal verbs

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