Which of the following is an example of a barrier to entry

How do scientists think that gravity affected the formation of our solar system?

Elements in group 2 are all called alkaline earth metals. what is most similar about the alkaline earth metals?

The human activities in two locations are described below: location a: rampant use of plastic containers location b: excessive use of pesticides and fertilizers which statement is most likely true? location a will have poor air quality because plastic is biodegradable. location a will experience water scarcity because plastic absorbs moisture. the population of honeybees will increase in location b because production of crops will increase. the population of fish in location b will decrease because the water is contaminated.