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.