For which of the following situations is the independent groups t-test appropriate (if inappropriate, why?):

a. The independent variable is infant birth weight at one week (normal vs high); the dependent variable is resting heart rate.

b. The independent variable is radiation treatment on throat cancer patients (one group getting a low dose and the other a high dose treatment); the dependent variable is white blood cell count.

c. The IV is infant birth weight (grouped as low vs high); the DV is number of days absent from school in first grade.

d. The IV is marital status (single vs divorced vs married); the DV is a happiness score, based on a 50 point scale.