What is the nature of the genetic mutation that causes lactose intolerance?

What is the nature of the genetic mutation that causes lactose intolerance?
  A. It is a dominant mutation that prevents lactase production.
  B. It is a dominant mutation that causes a decline in adult lactase levels.
  C. It is a recessive mutation that prevents lactase production.
  D. It is a recessive mutation that causes a decline in adult lactase levels.
  E. It is an X-linked mutation that prevents lactase production.

Question 2

What substance accumulates in the blood of people with galactosemia?
  A. Galactose
  B. Glucose
  C. Lactose
  D. Galactose-1-phosphate
  E. UDP galactose