The periodic table is composed of and
a. periods and rows
b. groups and columns
c. molecules and groups
d. groups and periods

D. groups and periods

Explanation:

In groups  the elements have the same electronic configuration in the last electronic shell and we expect that they will have similar chemical properties.

In periods the electronic configuration is increasing with one electron as we proceed from left to right and so the chemical properties will vary significantly.

answer

i think the answer is a) as air pressure in an area increases, the density of the gas particles in that area decreases.

hope it

under a microscope, cancer cells may look very different from normal cells. they often have different sizes and some may be larger than normal while others are smaller. cancer cells are often abnormally shaped and the control centre of the cell (the nucleus) may have an abnormal appearance.

i think? ?