在低倍镜下找到目标后，可以直接换用高倍镜观察吗？
不可以。应先将目标移至视野中央，再使用高倍镜观察。
Mary made coffee ________ her guests were finishing their meal.[ ]
A. so that
B. although
C. while
D. as if
粉尘排放浓度标准是多少？
