问题如下:
The longest of the widely recognized cycles was identified by Nikolai Kondratieff in the 1920s. The economic cycle has a period of:
选项:
A. 20 years.
B. 54 years.
C. 74 years.
解释:
B is correct. The economic cycle has a period of 54 years and is known as Kondratieff Wave.
老师,这道题不明白?请解释一下