Students at Warlock High are allowed to sign up for one social studies class each year. The numbers in each grade level signing up for various classes for the next school year are given in the following table:

Grade	US History	Civics	World History	Economics	Total
10th	75	10	125	5	215
11th	130	85	75	60	350
12th	35	150	50	105	340
Total	240	245	250	170	905

Part A: What is the probability that a student will take Civics? (2 points) Part B: What is the probability that a 10th-grader will take either US History or World History? (2 points) Part C: What is the probability that a student will take Economics given that he or she is in the 10th grade? (2 points) Part D: Consider the events "A student takes Civics" and "A student is a 12th-grader." Are these events independent? Justify your answer. (4 points)