For Each of the Following Questions, Determine Whether the Given

Multiple Choice

For each of the following questions, determine whether the given formula is a wff or not. If it is a wff, indicate its main operator.
-∼[(R • S) ⊃ U] ⊃ {{∼U ⊃ [R ⊃ (S ⊃ T) ]}

A) It's a wff. The main operator is the first ⊃, reading left to right.
B) It's a wff. The main operator is the first ∼, reading left to right.
C) It's a wff. The main operator is the second ⊃, reading left to right.
D) It's a wff. The main operator is the third ⊃, reading left to right.
E) Not a wff