单选题：根据以下内容，回答题。In addition to the established energy sources su

根据以下内容，回答题。
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 21in that they are both renewable. 22, hydropower is more widely used than tidal. In23, a substantial amount of electricity is already produced in HEP(hydroelectric power)stations worldwide,24tidal stations are still in the very early25of development.
As far as geographical26is concerned, HEP projects are to be found on lakes and rivers, while tidal27are constructed only at river mouths where tidal 28is great. Unfortunately these are29in number. At present HEP stations are found mainly in Norway, Canada, Sweden and Brazil, whereas tidal plants are in30in France, Russia and China.
As regards capital 31 , both require very high investment. On the other hand, generating 32are quite low in both cases. In fact, a large scale HEP plant is capable of producing power more33than conventional sources, such as coal, oil and nuclear plants. Tidal power also compares34with nuclear and oil-generated electricity,35the amount of money on production.36HEP stations, tidal constructions have a long life37. It is estimated that they can operate for over 100 years. With respect to38of supply, tidal stations 39from HEP ones in that they often can only supply power40. HEP stations, however, provide a constant supply of electricity.
A．compatible
B．parallel
C．similar
D．identical