问题
单项选择题
焊接黑色金属材料时，烟尘的主要成份是铁、硅、锰。焊接其它不同材料时，烟尘中尚有铝、氧化锌、钼等。其中主要有毒物是（）。
A、铝
B、锌
C、钼
D、锰
答案
参考答案：D
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焊接黑色金属材料时，烟尘的主要成份是铁、硅、锰。焊接其它不同材料时，烟尘中尚有铝、氧化锌、钼等。其中主要有毒物是（）。
A、铝
B、锌
C、钼
D、锰
参考答案：D
| 根据对话内容从方框内所给的选项中选出最佳答案，使对话完整，符合逻辑，句义通顺。有多余选项。 | |
B: Yeah. 1.______ A: Nervous about what? B: I don't know many of the customs and manners in the USA. 2.______ A: Sure. B: 3.______ A: Well, it's important to be on time when you're invited for dinner. 4.______ Americans expect their guests to be on time. B: Then how long may I stay there? A: 5.______ Or you seem to have come only for the meal. When your friends seem to be getting tired and running out of things, it's time to leave. The next day, call or write a thank-you note to say how much you enjoyed the evening. |