小科同学将数枚一元硬币放在两根平行的条形磁铁上，搭成了一座漂亮的“硬币桥”，如图所示．

根据句意及首字母提示完成单词。 
It's too hot,  we need to drink more w____. 
Mr. Black looks u____ ,  but he is a really good man. 
—How is the salad?  —Very d____.
—Where is the post office?   —It's at the c____ of the street. 
The movie Avatar is great.  We d____to see it again.

已知圆C和y轴相切，圆心在直线x﹣3y=0上，且被直线y=x截得的弦长为2$\sqrt{7}$，求圆C的方程．