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?

Part B: What is the probability that a 10th-grader will take either US History or World History?

Part C: What is the probability that a student will take Economics given that he or she is in the 10th grade?

Part D: Consider the events "A student takes Civics" and "A student is a 12th-grader." Are these events independent? Justify your answer.