Another name for these two words is "constant" and you want to have a "constant", because you want something to compare your experimental group to, to see whether data had changed or not. So you have placebos or a double- blind to compare your experimental group to it and also so you know you don't have a bias or anything in the study.
Answer:
Object 3 has greatest acceleration.
Explanation:
Objects Mass Force
1 10 kg 4 N
2 100 grams 20 N
3 10 grams 4 N
4 1 kg 20 N
Acceleration of object 1,
Acceleration of object 2,
Acceleration of object 3,
Acceleration of object 4,
It is clear that the acceleration of object 3 is 
and it is greatest of all. So, the correct option is (3).
Answer: A hymn which accompanies religious observances and rituals. And others like guitar, violin, flute, harp and the organ
Explanation: Gradually people instructed the natives not only in singing but also in playing various instruments like guitar, violin, flute, harp and later on, the organ.
A neutral atom is simply an atom that has no charge.
