THE BAG WAS HEAVY, SO WE COULD NOT TAKE IT WITH USA. IF THE BAG WAS NO...

Câu 29:

The bag was heavy, so we could not take it with us

A. If the bag was not heavy, we would take it with us

B.

Had the bag not been heavy, we would have taken it with us

C.

If had the bag not been heavy, we would have taken it with us

D.

Unless the bag had not been heavy, we would have taken it with us

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate

the correct answer to each of the questions

About fifty years ago, plant physiologists set out to grow roots by themselves in solutions in

laboratory flasks. The scientists found that the nutrition of isolated roots was quite simple. They

required sugar and the usual minerals and vitamins. However, they did not require organic

nitrogen compounds. These roots got along fine on mineral inorganic nitrogen. Roots are

capable of making their own proteins and other organic compounds. These activities by roots

require energy, of course. The process of respiration uses sugar to make the high energy

compound ATP, which drives the biochemical reactions. Respiration also requires oxygen.

Highly active roots require a good deal of oxygen.

The study of isolated roots has provided an understanding of the relationship between shoots

and roots in intact plants. The leaves of the shoots provide the roots with sugar and vitamins,

and the roots provide the shoots with water and minerals. In addition, roots can provide the

shoots with organic nitrogen compounds. This comes in handy for the growth of buds in the

early spring when leaves are not yet functioning. Once leaves begin photosynthesizing, they

produce protein, but only mature leaves can "export" protein to the rest of the plant in the form

of amino acids.