Dozens of scientific groups all over the world have been ___________the goal of a practical and economic way to use sunlight to split water molecules.

单项选择题Changing from solid to liquid, water takes in heat from all substances near it, and this___________ produces artificial cold surrounding it.

单项选择题The data (received) from the (two spacecrafts) whirling around Mars (indicates) that there is much evidence that huge thunderstorms (are occurring) about the equator of the planet.