Which statement describes how a machine can help make work easier? It can put out more force than the input force by decreasing the distance over which force is applied.
It can increase the amount of work performed if the output force is in the same direction as the input force.
It can apply a greater output force over a greater distance compared to the input force and distance.
It can increase the distance over which output force acts by applying less output force than input force.

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.