I am only concerned with questions 4 and 5. For 4, I said you couldn't assume that plane S intersects plane T at line BC. The arrowheads, one at each end of the line, are not really indicative of any 'property' of line AB as it (the property) pertains to plane S or plane T; given the arrowheads were the only thing I saw could give any information about the line, I concluded you couldn't make the assumption that it is the intersection of plane S and plane T.
As for question 5, I couldn't explain why the two were perpendicular.