What is the most difficult part of a controlled experiment?
testing only one variable
testing two variables
testing multiple variables
testing zero variables

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled

Wich is not standing in the way of astronomers getting a good view of different star

Brepresent the dominant allele for brown fur, and b represents the allele for white fur. if two rabbits with the genotype bb reproduce, what are the possible phenotypes for their offspring