单选题 They were ______ in their scientific research, not knowing what happened just outside their lab.
【正确答案】 C
【答案解析】[解析] immerse意为“沉浸，使陷入”，be immersed in意为“专心致志于”，符合题意。submerge指“浸没，淹没”；drown指“溺死，淹死”；dip指“浸，蘸，沾”。句意：他们专心致志于科研，不知道实验室外发生了什么。