题干
The farmer is very busy because he's so _______ sheep to keep and so ______ work to do every day.
A：much; many
B：many; much
C：many; a lot
D：a lot; much
答案(点此获取答案解析）
B
对任意自然数x，y均满足：
，且
，则
等于（ ）
…的递推公式是