work hard in还是work hard at？

work hard at sth.
work at [简明英汉词典]
从事, 致力于, 钻研

work in [简明英汉词典]
v.插进, 引进, 配合

work at
从事, 致力于, 钻研
work in
插进, 穿入
搀, 加入
为...安排适当的时间
揉擦
想表达“努力做……事情”，还是用work hard at

work hard at office
work hard in the factory

work hard at sth.

work at
从事, 致力于, 钻研
work in
插进, 穿入
搀, 加入
为...安排适当的时间
揉擦
想表达“努力做……事情”，还是用work hard at