Solution
= Solution
\b[Allowed.] A single $t$-channel <W boson> mediates the <weak charged current> transitions $u\to d$ and $\bar c\to\bar s$. The amplitude is proportional to the <Cabibbo-Kobayashi-Maskawa matrix> product $V_{ud}V_{cs}^*$.
= Solution
\b[Allowed.] A single $t$-channel <W boson> mediates the <weak charged current> transitions $u\to d$ and $\bar c\to\bar s$. The amplitude is proportional to the <Cabibbo-Kobayashi-Maskawa matrix> product $V_{ud}V_{cs}^*$.