Which of the Following Is True or Accurate About the Transition

Which of the following is true or accurate about the transition to renewable energies?

A) Coal can continue to be used as long as we keep atmospheric CO₂ levels below 800 ppm.
B) Natural gas,which produces less CO₂ when burned,can serve as a "bridge energy" to the development of enough renewable energies.
C) At present none of the U.S.states has any requirements or goals for the transition.
D) Venture capitalists have invested very little in global renewable energy because of uncertainty about its effectiveness.