What does it mean to be selectively or semi permeable?

Which describes radioactive decay of a substance

Viruses are different from bacteria in that they can remain dormant on non-living surfaces they can be found just about anywhere they can infect just about every form of life

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