求解a为什么不对

问题如下：

选项：

A.sets an explicit price on greenhouse gas emissions.

B.mandates similar levels of emissions reductions for all actors.

C.creates an economic incentive for emissions reductions to occur at the point of least cost.

解释：

Cis correct because "an ETS [emission trading system] is a systembased on the exchange of permits for emission units, where actors who exceedtheir emissions limits are required to buy permits from those that have emittedless. The overall quantity of emissions is fixed, and market mechanisms areused to set their price. In theory, this creates an economic incentive foremissions reductions to occur at the point of least cost; rather than mandatingsimilar levels of reductions for all actors, price discovery helps reward thosethat can afford to reduce more."

Ais incorrect because "carbon taxation takes a different approach [comparedto ETS] by directly setting an explicit price on GHG emissions (e.g. per tonneof CO₂)."

Bis incorrect because an ETS "creates an economic incentive for emissionsreductions to occur at the point of least cost; rather than mandating similarlevels of reductions for all actors, price discovery helps reward those thatcan afford to reduce more."