Answer:
<em>The correct option is D)  How is the number of frogs in Massachusetts affected by pollution</em>
Explanation:
A scientific question can be described as a question which can be answered through the scientific method of research. Based on the scientific question, a hypothesis can be formulated. For example, for the option D, the hypothesis can be 'if the pollution increases, then the number of frogs decreases.' A hypothesis is a tentative statement which can be tested through experiments. Based on these experiments, results are formulated and conclusions are drawn. The question mentioned in option D can be answered through this method hence, it is the correct option. 
 
        
             
        
        
        
Answer:
Neurotransmitters
Explanation:
Neurotransmitters are the chemicals present in the body used for the propagation of action potential. These neurotransmitters are also known as the body chemical messengers.
Neurotransmitters are stored in the neural cells. These chemicals are generally released when the cell is stimulated by the specific signal. The effect of neurotransmitter may be excitatory or inhibitory.
Thus, the answer is option (4).
 
        
             
        
        
        
Answer:
A
Explanation:
A)Chromosomes assort independently, and crossing-over occurs.
 
        
             
        
        
        
As any other ancient civilization, the Sumerians were traders as well. And they had a few good reasons to do this. 
Because they traded, their trading partners were less likely to attack them, because it would hurt their economy as well. Furthermore, they didn't produce everything they needed and traded those goods with goods which they produced too much of. 
And lastly, through trade they could also get exotic goods which they would have never gotten otherwise.