"Renewables are not without their drawbacks. Solar and wind farms cannot generate much electricity on cloudy or still days. As intermittent energy sources, they require vast systems to store the energy they produce, or must rely on the rest of the electrical system for backup. And despite federal subsidies to spur technological innovation, renewable sources have not become economical enough to seriously challenge fossil fuels in an open market."
3. According to Document C, all are drawbacks of reewables except which of the following?
a. They are intermittent energy sources.
b. They are not cost-efficient.
c. They rely on traditional electricity sources.
d. They are worse for the environment.