A. The PDPA was a socialist party. USSR was providing a military support to the PDPA. Not the US.
B. I found one statemant in Wiki that says that US actually supported anti-government movements. I can't really tell that it was so (that americans supported exactly the Mujahideen movement) but everything fits together 'cause other response options in this test don't fit.
C. Babrak Kamal was one of PDPA's leading members. It's obvious that US didn't support him.
D. Naah.