Let \( A \) and \( B \) be independent events such that \( P(A)=p \), \( P(B)=2p \). The largest value of \( p \), for which \( P \) (exactly one of \( A, B \) occurs) \( = \frac{5}{9} \), is:
\( \frac{5}{12} \)
\( \frac{2}{9} \)
\( \frac{4}{9} \)
\( \frac{1}{3} \)