A group of 500 people are selected at age 2 no0 and followed for 15 years. The people who go on to develop a certain type of cancer are compared those who do not. The researchers attempted to determine different factors that could increase cancer risk

convalent bond :

is a chemical bond formed by the sharing of electron between 2 atoms.

it is the direct chemical bond between 2 atoms.

in bond formation atoms are involved here.

electrovalent bond:

is a chemical bond defined as electroststic attraction between 2 atoms.

it is the electrostatic attraction between 2 atoms.

in bond formation, ions are involved here.

hope it

and ur welcm

: )

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.