Answer:
An external stimuli is a stimulus that comes from outside an organism and causes a reaction.An internal stimuli is a stimulus that comes from inside an organism.
The molecule with same molecular formula but different arrangement of atoms is said to be an isomer.
When 2,2-dimethylbutane reacts with chlorine in the presence of light gives three isomers that is 
(3-chloro-2,2-dimethylbutane), 
(1-chloro-2,2-dimethylbutane) and 
(1-chloro-3,3-dimethylbutane).
In above case, the molecular formula of all isomers are same i.e.
but chlorine is arranged in different positions of carbon. Thus, results isomers.
The reaction is shown in the image.
Answer:
They are better because they are more usable than Plastic and reusable water bottles are better for the planet!
Explanation:
Comets are usually formed of ice and other suave debris, while asteroids typically contain metals.
<span>Scientists have determined that the center of the earth is 6371 km below the surface. But how has this been determined? Many people might answer that question by saying scientists can drill into the Earth with machines. However, the drilling rigs that scientists use can only drill about 20 km in the Earth which is not very deep! In other words, we can only drill into upper part of the crust of the earth. Extremely high temperatures and pressures within the Earth make drilling into it very difficult</span>
