In the Coin Game, you toss three coins at the same time. You win only if the 3 coins are all showing heads, or if the 3 coins are all showing tails. If you play the game once only, what is the probability of winning? 
选项为:A:$\frac{1}{6}$  B:$\frac{1}{3}$  C:$\frac{2}{27}$  D:$\frac{2}{3}$  E:$\frac{1}{4}$  请回答其中一个选项.