I just took that double attack test #1 and I think there is something inacurrate there.
Question 15 is this:
and the answer marked as correct is:
very nice and sufficent to win, but i think this is even better:
because if black captures the bishop, there is a family check with Ng5+ and if not, white can still carry out the Qxe4 idea.
P.S. I think I have found another flaw there, Question 20 is: "what is the worst move now?" and on marking the blunder-move, I get a wrong there.
Also, in Question 10 the Move marked as correct is B