【单选题】

In addition to the established energy sources such as gas, coal, oil and nuclear, there are a number of other sources that we ought to consider. Two of these are hydroelectric and tidal power.

These two sources are (21) in that they are both renewable. (22) , hydropower is more widely used than tidal. In (23) , a substantial amount of electricity is already produced in HEP (hydroelectric power) stations worldwide, (24) tidal stations are still in the very early (25) of development.
As far as geographical (26) is concerned, HEP projects are to be found on lakes and rivers, while tidal (27) are constructed only at river mouths where tidal (28) is great. Unfortunately these are (29) in number.At present HEP stations are found mainly in Norway,Canada, Sweden andBrazil, whereas tidal plants are in (30) in France, Russia andChinA、
As regards capital (31) , both require very high investment. On the other hand, generating (32) are quite low in both cases. In fact, a large scale HEP plant is capable of producing power more (33) than conventional sources, such as coal, oil and nuclear plants. Tidal power also compares (34) with nuclear and oil-generated electricity, (35) the amount of money on production. (36) HEP stations, tidal constructions have a long life (37) . It is estimated that they can operate for over 100 years. With respect to (38) of supply, tidal stations (39) from HEP ones in that they often can only supply power (40) HEP stations, however, provide a constant supply of electricity.
A．develop
B．differ
C．depart
D．derive