1. Has it been tested and observed numerous times by more than

one group of scientists?

Yes, it has.

Explanation:

Replicability of an experiment holds great importance in the scientific world. Different groups of scientists ought to be able to replicate a certain experiment to achieve the same results/conclusions as the first team of scientists did. This is essential to prove that the findings are credible and did not just occur by chance, which is the case here too.

i am positive it is c. condensing but i may be wrong