exist simultaneously; exist side by side; 同时存在
happened at the same time; coincide; concur; synchronism 同时发生
The task is arduous; besides, there's not much time. 任务艰巨,同时时间又很紧迫。
牛津高阶第八版
美国韦氏词典
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维基百科 (自由的百科全书)