应该用一般过去时。因为at the beginning意为“在开始的时候”，一般用来叙述事情发生的先后顺序。除此之外，还有at first，then，at last，finally，immediately，at once，eventually，suddenly等。如：At the beginning the house caught fire. Immediately some people rushed out and cried for help. Finally some firefighters came and put it out.