Which represents a force pair?

A. A golf club hits a golf ball. Gravity pulls the ball back down to Earth.
B. A book pushes down on a table, and gravity pulls the book toward the floor.
C. A boy's foot pushes down on a bicycle pedal. The pedal pushes up on his foot.
D. A person's foot pushes on the floor, and the person's weight pushes on the floor.

i think the answer is b.

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.