There may be life on Mars.We know m_____ about Mars than about any other planet.But astronauts are
still g_____ about many things.For wxample,we think that on Mars there may be change of weathwe d_____ the year.Our own weather changes f_____ winter to summer .P______it is the same on Mars.In Mars' midsummer we can s____ brown places on the planet.In midwinter these places are w____.So some scientists b_____ that plants grow on Mars during midsummer and change color in winter.They are not s______ if there are green fields on Mars.But some people think there is some k____ of life there.