【正确答案】 A

【答案解析】[理由] (A)number表“数目”，须与复数名词连用：
a large number of+复数名词+复数动词 许多的……
the number of+复数名词+单数动词 ……的数量
[例] A large number of people have applied for the job.
(已有许多人应征了这份工作。)
The number of jobless people in this area has increased.
(这个地区的失业人数已经增加。)
*此句因真正的主语是The number，故动词使用单数动词has increased。
(B)amount表“量”，须与不可数名词连用：
a large amount of+不可数名词+单数动词 大量的……
the amount of+不可数名词+单数动词 ……的量
[例] A large amount of money is needed for the project.
(这个计划需要一大笔的钱。)
The amount of the bill is $100．
(这份账单的金额是100美元。)
*此句因真正的主语是The amount, 故动词使用单数动词。
(C)percent表“百分比”，之前须加明确数字：
[例] The salesperson gave me a discount of 20 percent off the regular price
(那名售货员用平常价的8折卖给我。)
原句空格后有复数名词staff members(员工)，根据语意及用法，(A)应为正选。