【正确答案】 B

【答案解析】[解析] 画线部分all at once意为“突然”。A项for a long time意为“很长时间，很久”；例：We haven't corresponded for a long time. 我们好久没有通信了。B项suddenly意为“突然”；例：The boat suddenly rocked and pitched him into the water. 小船突然晃起来，把他甩到水里。C项for no reason意为“无缘无故，无端”；例：Our burglar alarm is often going off for no reason. 我们的防盗报警器不知什么原因常常失灵。D项quickly意为“迅速地，很快地”；例：A letter sent airmail will get to Europe quickly. 寄往欧洲的航空信件会很快到达的。故本题选B。