In a covalent bond:

a. An atom gains one or more electrons from another atom to gain stability.
b. Adjacent atoms share a single electron.
c. An atom loses electrons to another to gain stability.
d. Atoms share one or more pairs of electrons.

The correct answer is d. Atoms share one or more pairs of electrons.

Explanation:

In a covalent bond, electrons of the last energy level are shared, to reach the octet (except for the Hydrogen that reaches its stability with 2 electrons). This type of bond occurs between two nonmetallic compounds. Example: H202 (hydrogen peroxide) formed between oxygen and hydrogen.

the leaf is an organ of a typical plant, and the main functions are to complete photosynthesis and allow the plant to exchange gas, just like how we have the respiratory system. leaves have the stomata, which collects maintains co2 and o2 levels. this is necessary for cell metabolism. the leaf also collects sunlight using chloroplasts. succinctly, leaves own a pivotal role in sustaining plant life.