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which statement is true?

spiral and elliptical galaxies have gas and dust between stars while irregular galaxies do not.
spiral and irregular galaxies have gas and dust between stars while elliptical galaxies do not.
irregular galaxies have gas and dust between stars while elliptical and spiral galaxies do not.
elliptical galaxies have gas and dust between stars while irregular and spiral galaxies do not.

When creating a graph, the goes on the x axis and the goes on the y axis. a. dependent variable, independent variable b. experimental group, control group c. independent variable, dependent variable d. control group, experimental group

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

The large increase in atmospheric carbon dioxide in the last 50 years most likely comes from a. an increase in cellular respiration b. increased decomposition by bacteria c. an increase in the burning of fossil fuels d. an increase in photosynthesis