A, hypothesis, theory) is scientific knowledge established through direct observation and remains constant. scientific knowledge can change when scientists conduct experiment, generate hypothesis, hold different views).

1. The first choice is correct which is fact.

2. The first choice which is conduct experiment is correct.

A fact is nonscientific observation based law which can not be changed because any experiment could not be conducted to test it. As the sun sets in the west.

While a scientific theory or observation can be changed because experiment can be conducted on these. As dengue is caused due to a virus.

elements make up everything, and they combine to make compounds.

the answer is c