Answer: decreases alertness and low mental awareness
Explanation: when asleep although we still experience some level of consciousness, it fades as we fall deep into sleep. Mental awareness during this period is also undergoes major changes through an orderly progression of sleep stage.
I think it is B, because that is my best guess!
Answer: A systematic sampling method.
Explanation.
The purpose s to obtain data that closely resembles that of the entire population. Because this is impractical, random sampling is used.
After determining what a reasonable sample size will be, the size of the population is divided by the sample size to obtain a sampling interval.
The random sample is obtained from the population at the calculated sampling interval.
Answer:
The widening channel of a river where it meets the sea, mixing fresh water and salt water