Why is nitrogen fixation necessary?
O
A. Respiration uses nitrogen that is attached to oxygen.
O
B. Most plants use single nitrogen atoms, not N, molecules.
O
C. Photosynthesis requires excess nitrogen.
O
D. Plant life cannot use nitrogen atoms unless they are fixed into
pairs.

D. Plant life cannot use nitrogen atoms unless they are fixed into

pairs.

Explanation:

Nitrogen is present in very high concentration in the atmosphere about 78 percent. This nitrogen cannot used by the plants due to the presence in molecular form. This atmospheric nitrogen fixes by bacteria called Nitrogen fixing bacteria which is present in the roots of leguminous plants. This atmospheric nitrogen is converted into nitrates which is used by the plants for making amino acid.

answer: d. load

a river's load refers to the natural phenomena in which the sediments, rocks   stones, boulders and other deposits are removed and picked from the bottom bed of the river due to the abrasion resulted by the high speed water current.