The area in which surface water flows into a single stream is called a. a delta b. a headwater c. a watershed d. a stream system

Option C, a watershed

Explanation:

A catchment area also known as water shed is a parcel of land where all streams combine to form one single stream. These numerous stream combine into one single stream in order to drain into a common/single drainage point i.e either a sea or ocean. It is also known as a drainage basin. Along with river streams, water from from all different precipitation mode with in a region  also drain into the single stream in a watershed

Hence, option c is correct.

1.the evidene of the reaction

2.yes

3.yes

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).