added ball proportion

• 加球配比

added ball proportion的用法和样例：

例句

1. A control set of traditional RPC mix proportion was also used for comparison.
   并与国内一般常用配比做比较。
2. The influences of the reactant proportion and reacting condition on the yield were also studied.
   研究了反应物配比及反应条件对反应产率的影响。