The relationships between a community of plants and animals and their environment are known as a(n)

Ecosystem

reason -

An ecosystem consists of both abiotic and  biotic components that interact with in themselves and the surrounding physical environment. All these components are interlinked and connected through various food , nutrient and energy cycle to maintain the stability with in the ecosystem. All elements and organisms are essential to the functioning of an ecosystem and none of them can be ignored or replaced with the other.

B. is the correct answer. - Pyruvate is decarboxylated, acetyl reacts with coenzyme A, forming NADH + H+

During the Krebs Cycle ( also known as the Citric Acid Cycle) the Pyruvate molecule decarboxylated ( meaning it lose a carbon a carbon dioxide molecule) and forms the molecule acetyl- coenzyme A also known as (acetyl CoA). Furthermore, NAD+ ( nicotinamide adenine dinucleotide)  reacts with H+ to form NADH