The correct answer is "1900-2000".
The graph represents hydroelectric power (y axis) along time (x axis). From 1950 to 1970 the usage of this type of power grew steadily. From this moment on, some peaks and valleys can be observed in the graph. Although other maximums had been registered in the usage of hidroelectric power, the highest peak took place in the decade of the 90s-00s. This peak was followed by the worst decline experienced since 1970.