How is everything going on with you in America?-Quite well.N

How is everything going on with you in America?-Quite well.Not so smoothly as I hope,_____
A.either B.too C.though D.yet 我觉得C也是可以的.应该.
接着看这道题.Yesterday I was walking downstairs wehn I missed my foot and had a bad fall,nothing serious,though.这个题目靠的是THOUGH.though和Yet都放在句尾,并且两个单词存在的句子中都含有否定含义.有什么区别?