—Guang'an is a beautiful city, isn't it?
—Yes. There are about two _______ visitors here every week.
A:thousands of
B:thousands
C:thousand
D:/
在反应x+2y=R+2M中,当1.6gx与y完全反应后,生成4.4gR,且反应生成的R和M的质量之比为11∶9,则在此反应中y和M的质量之比 ( )