Canyons, caverns, channels, and valleys all form because of erosion by water. Which landform listed is mainly formed because of erosion by groundwater?
A a broad valley
B. a narrow canyon
C. a human-made channel
D. an underground cavern

The model illustrates a process by which a substance is taken up by a cell

The body is protected against harmful flu viruses by

Researchers randomly divide participants into groups. each group takes a different amount of omega-3 fatty acid supplements daily for a month. one group receives a placebo. the researchers measure the impact on cholesterol levels in the blood. what is the purpose of random assignment in this experiment? a, to produce treatment groups with similar characteristics b, to ensure that all people with high cholesterol have an equal chance of being selected for the study c, to increase the accuracy of the research results and prevent skewness in the data