Place a piece of dark metal and a piece of light-coloured wood or cloth of about the same size side by side in the sunlight on a bright afternoon. Touch them after a while, or set a thermometer on each. You will find the dark metal is hotter, though both have been warmed by the sun for the same length of time. This is because some things absorb(吸收) more heat from the sun than others, lying in their colour, form and material. A ploughed field of black soil becomes heated faster than a field of corn. The cornfield in turn absorbs more heat than a lake or a pond. This curious fact about heating explains the most common thunderstorms(雷雨), the kind seen on a summer afternoon.

4. From the passage we know________.

A. the colour of wood or cloth is lighter than that of metal

B. if you stand in a cornfield you'll feel hotter than in a ploughed field

C. when the sunlight is not quite bright light-coloured wood absorbs more heat than dark metal

D. if you put something in the sun, its temperature will be affected by its color, form and material

5. The underlined word "thermometer"probably means________.

A. something that is like a stove

B. an instrument for measuring temperature

C. a tool which is used to heat

D. a watch which can be started and stopped

6. The last sentence of the passage leads us to conclude that________.

A. thunderstorms break out over a lake

B. thunderstorms have something to do with the heat from the sun

C. thunderstorms are often seen in winter, too

D. thunderstorms have never happened in dark materials