1965 AHSME Problem 17

Given the true statement: The picnic on Sunday will not be held only if the weather is not fair. We can then conclude that:

\begin{array}{l} \textbf{(A)}\ \text{If the picnic is held, Sunday's weather is undoubtedly fair.} \\ \textbf{(B) }\ \text{If the picnic is not held, Sunday's weather is possibly unfair.} \\ \textbf{(C) }\ \text{If it is not fair Sunday, the picnic will not be held.} \\ \textbf{(D) }\ \text{If it is fair Sunday, the picnic may be held.} \\ \textbf{(E) }\ \text{If it is fair Sunday, the picnic must be held.} \end{array}

Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.