Logic/Discrete Mathematics

Question

Suppose one wishes to prove that "if all X are Y, then all Z are W". To do this, it would suffice to show that

1. All Z are X, and all Y are W.
2. All X are Z, and all W are Y.
3. All Y are Z, and all W are X.
4. All Z are Y, and all X are W.
5. All Y are X, and all W are Z.
6. All X are Z, and all Y are W.
7. All Z are X, and all W are Y.

Answer 1

option #7: All Z are X, and all W are Y.