Can you check my homework? (don't think I'd posted before)

38. How does natural selection lead to evolution?
a. Organisms mutate to adapt to their environment.
b. Helpful traits accumulate among surviving members of the species.
c. Overproduction provides food for stronger members of the species.
d. Environmental changes kill stronger members of the species.
Ans: B

46. In terms of the theory of natural selection, which explains why giraffes have come to have such long necks?
a. Stretching to get food in high trees made their necks longer, and this trait was passed to offspring.
b. Giraffes prefer other giraffes that have long necks as their mates.
c. Giraffes born with the longest necks stayed alive when food was scarce and passed this trait on to their offspring.
d. Giraffe food contains hormones that cause their vertebrae to lengthen
Ans: A or C?

49. Select ALL of the items below that provide evidence for evolution:
a.similar development of embryos
b.homologous traits
c.the fossil record
d.DNA similarities
e.Carbon dating
f.examples of evolution occurring over observable periods of time (such as peppered moths)
Ans: A,B,C,D,F

Experiment A: Four groups of rats are first massed and then fed identical diets except for the amount of vitamin A they receive. Each group gets a different amount. After three weeks on the diet, the rats’ masses are measured again to see if there has been a decrease.
57. What is the manipulated (independent) variable?
Ans: vitamin A

58. What is the responding (dependent) variable?
Ans: mass

59. What is the controlled variable? Ans: diet

The first one is b.