________ those college students come to see the old man who has no son or daughter．They find he grows weaker ________．

1. A.
   Year after year；year by year
2. B.
   Year by year；year after year
3. C.
   Year after year；year after year
4. D.
   Year by year；year by year

________ those college students come to see the old man who has no son or daughter．They find he grows weaker ________．

A．Year after year；year by year

B．Year by year；year after year

C．Year after year；year after year

D．Year by year；year by year