阅读下列短文, 从每题所给的A、B、C、D四个选项中选出最佳选项。
The greening of planes, trains and automobiles

Moving goods and people around the world is responsible for a large part of global CO2 emissions (排放). As the world races to decarbonize everything, it faces particular problems with transportation — which accounts for about a quarter of our energy-related greenhouse gas emissions. Here’s the breakdown of the emissions in 2018 for different modes of transport.

The fuels for transport need to be not just green, cheap and powerful, but also lightweight and safe enough to be carried around. Each mode of transport has its specific fuel needs. Much is still to be settled, but here are some of the solutions to get us going green.
PLANES — Synthetic hydrocarbonsThe hardest sector to decarbonize is aviation. One long-term option for sustainable fuel for planes is to make hydrocarbons from recycled air. CARS — BatteriesBatteries are energy-efficient and electric cars can plug into existing systems and services. New solid-state batteries will take a car farther on a single charge.

This energy transition (变革) is global, and the amount of renewable energy the world will need is “a little bit mind-blowing,” says mechanical engineer Keith Wipke at the National Renewable Energy Laboratory. It’s estimated that the global demand for electricity could more than double by 2050. Fortunately, analyses suggest that renewables are up to the task. “We need to speed up the development of green energy, and it will all get used,” says Wipke.

TRAINS — ElectricitySome trains are already electrified through rails or wires; others can be made electric in pretty simple ways.	TRUCKS — Hydrogenfuel cells Hydrogen fuel cells are a lighter choice than batteries for trucks, but making green hydrogen is expensive.	SHIPS — Liquid ammoniaLiquid ammonia is easy to keep and transport, but it is hard to ignite (点燃) and requires an engine redesign.

Which mode of transport can go green comparatively easily?