如图，用两根等长轻绳将木板悬挂在竖直木桩上等高的两点，制成一简易秋千。某次维修时将两轻绳剪去一小段，但仍保持等长且悬挂点不变。木板静止时，F₁表示木板所受合力的大小，F₂表示单根轻绳对木反拉力的大小，则维修后

A．F₁不变，F₂变大

B．F₁不变，F₂变小

C．F₁变大，F₂变大

D．F₁变小，F₂变小

As soon as he got to the office, he _____ the students' papers. [ ]

A. got down to correct

B. got down to correcting 　

C. set down to correcting

D. sit down to correcting