The number of the workers in this small company has grown 1000 to 1200．This means it has risen _______ 20 percent．
A.byB.atC.toD.with在线课程A
解析：
表达“变化了多少”用介词by。to表示“变化到某个程度”, 如：The number of the employees has risen to 1200。这道题说明的是增长了20％, 显然, 答案是by。其他介词均没有这种用法。正确答案是A项。