Ever since my brother graduated from the university, he _______ in the present company for 15 years and he is now chief engineer of the company.   [ ]

A. worked  

B. has been working  

C. is working    

D. works

（10分）一质量为m ="40" kg的小孩站在电梯内的体重计上.电梯从t =0时刻由静止开始上升,在0到6 s内体重计示数F的变化如图所示.试问：在这段时间内电梯上升的高度是多少？取重力加速度g="10" m/s².