The answer is A because at a young age children will not understand and they need to learn at the appropriate level
When your hand hits the table the table will vibrate and your hand will be numb for two to three seconds
I think your answer is D
because you already said its not a B is a liquid and not a solid so its harder to have a chemical change C is solutions and D is compound and I know for a fact that a compound is a solid and if C is also a solid then that could also be a possible answer choice.
Let vb be the velocity of the motorboat and let vs be the velocity of the stream.
We know that when she drives upstream the velocity is 8 m/s, in this scenario the velocities point in opposite directions, then we have the equations:

When she drives downstream the velocites point in the same direction then we have the equation:

hence we have the system of equations:

Solving the first equation for the velocity of the boat we have:

Plugging this in the second equation we have:

Therefore, the velocity of the stream is 2 m/s