Answer:
Star formation occurs most rapidly in the spiral arms, where the density of interstellar matter is highest.
Answer:
C or 3
Explanation:
A: no they are called sources of sound. A is incorrect.
B: It does. Many people attest to this. But this is not a property of physics.
C: A media is required is the correct answer.
D: Dogs might. In general we don't.
I would pick C
Answer:

Explanation:
From the concept of fluids mechanics we know that if a tank has a hole at the bottom, the equation that we need to use is:

Since we know gravity and its hight

Answer:
4 km/hr
Explanation:
The computation of the actual velocity is shown below:
Because the path of its paddles is opposed to the current direction, the real velocity can be determined by deducting the current velocity to its velocity while paddling
So, the actual velocity is
= Upstream - downstream
= 19 km/hr - 15 km/hr
= 4 km/hr
As we can see it is in positive, so it is an upstream direction