正确答案: C

observed

题目：39___________

解析：C

查看原题

举一反三的答案和解析：

[单选题]Most Americans would prefer to keep their problems ________ themselves, and solve their problems ______ themselves.

to; by

[单选题]以下说法正确的是（ ）。

水溶性药物选择脂溶性基质

[单选题]It was a nice house, but ( )too small for a family of live.

rather

[单选题]—Why do you want to work for our company?—This is the job that I _______for.

have been looking

[单选题]使用显微镜观察洋葱根尖细胞染色体的基本步骤包括：①调节细准焦螺旋；②转换高倍镜；③把分裂中的细胞移至视野中央；④将洋葱根尖永久装片放在低倍镜下观察。正确的操作顺序是

④③②①

解析：使用显微镜观察洋葱根尖细胞染色体的基本步骤，正确的操作顺序应是先将洋葱根尖永久装片放在低倍镜下观察，找到分裂中的细胞，再移至视野中央，转换成高倍镜后，再调节细准焦螺旋，就可看到洋葱根尖细胞染色体。