Quark composition of Neutral Antikaon?

[opticaltempest]

I need to determine the quark composition of the neutral antikaon. Below is a copy of my multiple choice question.

http://img166.imageshack.us/img166/2025/quarksec1.jpg [Broken]

Here is my attempt at a solution:

First, a neutral antikaon is a meson. This means it must be composed of a quark-antiquark pair. A neutral antikaon has charge of 0 and strangeness of -1. From the six known quarks, the composition must be a strange quark and an antidown quark.

I tried selecting $$s \bar{d}$$ but that is incorrect. How?

For a table of needed quark properties, see http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/quark.html" [Broken]

 

[astrorob]

I refer you to;

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/kaon.html