Understanding Formal Depictions - Example 1 & 2

The correct solution is (D).

Statement I is incorrect:
If F1 = a, then the first question is answered “YES”. Then you come to the decision step below that. If F2 = a, then the second question is also answered “YES” and you go right to the next decision step. If F3 = d, this question is also answered “YES” and you come to decision Y. Hence it is possible that F1 = a and Y is selected, not X.

Statement II is also incorrect:
If F1 = b, you go right from the first decision step. The question in this decision step is “F2 = a?”. If F2 = b and you hence answer the question “NO”, you come directly to decision Z. Hence it is possible that F2 = b and Z is selected, not X.

The correct solution is (B).

Statement I is incorrect:
If F1 = a, then the first question is answered “YES”. Then you come to the decision step below that. Then you come to the decision step below that. If F2 = b, then the second question is answered “NO” and you move down and select X.

Statement II is correct:
The only way to decision Z is via the decision step at the top right (F2 = a?). If F2 = a, then the question is answered “YES” and you move to the decision step below, from where you can only go to X or Y.