什么是DWDM技术？
参考答案：
密集波分复用。波长间隔为0.8nm（在1.55μm波段对应100GHz频率间隔）的整数倍。
All the students in this school are required to________at least two lectures on how to study every month.[ ]
A. attend
B. take part in
C. join in
D. go in for
无论是真正的创造还是类似的创造，它们所表现出来的思维或认知能力在本质上相同。( )
