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.

c) 50% there are four chromosomes. after crossing over, 2 of the four have been changed. that means any gamete has a 2 in 4 chance or 50% chance of receiving the mutated chromosome.