Answer:E
Explanation:
This can be explained by Doppler effect which gives the relation between apparent Frequency and actual frequency when the source of sound is moving

where 



here
as observer is standing
when Ambulance is approaching then velocity of sound and velocity of ambulance have relative velocity thus denominator is less than and apparent frequency is more while when ambulance is going away then velocity of sound waves and velocity of observer is in opposite direction thus denominator is less than 1 and apparent frequency is less.
Thus 
In order to predict whether a star will eventually fuse oxygen into a heavier element, you mainly want to know about the star's mass.
<u>Explanation:</u>
Stellar evolution is procedure by which star experiences a succession of radical change during its lifetime. Depending upon the mass of stars, this lifetimes range from just two or three million years for most big to the trillions of years for a least massive, which is significantly longer or more than the age of universe.
All stars are conceived from falling billows of gas and residue, frequently called nebulae or sub-atomic mists. Throughout a large number of years, the protostar settles down into a condition of balance, turning out to be what is also known as the main- sequence - star.
Answer:
Please refer to the figure.
q1 is a negative charge, and q2 and q3 are positive charges. So, the force exerted by q1 on q3 is attractive, and the force exerted by q2 on q3 is repulsive, which means F13 is directed towards left, and F23 is also directed towards left.


The net force on q3 is the sum of these two forces:

Since both forces are directed towards left, their sign should be negative.