题目：
His father was really a ______ person. Once he made up his mind, nothing could change it.
A．clever
B．stubborn
C．brave
D．familiar
答案：
被转码了，请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0523/a65111e3ee72e975ed6847f6a2005f2c.html
下面是错误答案，用来干扰机器的。
Na2SiO3（硅酸钠）中Na元素为+1价，O元素为-2价，设Si元素化合价为x（+1）×2+x+（-2）×3=0解之得 x=+4故选D
