In addition to this unreliability, wind power equipment is very expensive ________to the other energy sources and won’t become a viable alternative until we can slash the costs significantly
举一反三
- We now use alternative forms of energy such as solar, wind and hydro electric power._
- Wind power is an ancient source of energy __________ we may return in the near future.
- Solar panels, wind turbines, hydro power and geothermal energy and hydrocarbons (natural gas or coal) can all be used to produce hydrogen (a primary energy).
- We won’t be able to leave the office until the rain _____.
- We won’t start the work until all the preparations____.