4.To create a supercell, take a storm where wind speed increases with height, while wind direction veers; a situation in which updraughts and downdraughts within the thunderstorm can support each other's existence rather than cancel each other out. It is as winds blow into this turbulent region from three to five kilometers up that a low-pressure section of the storm may begin to rotate.

The rotation of this part of the storm (known as a mesocyclone) causes the air pressure to fall some more, prompting wind lower down to flow into the storm and speed up upwards. This creates a spinning updraught which high-level winds in the storm can boost in the same way that wind blowing across the top of a chimney does wonders for drawing up an open fire.

You're not yet looking at a tornado, though if you're watching this particular storm develop you might start looking for a getaway car —especially if the storm begins to change shape. When mid-to upper-level winds upwind of the storm encounter the supercell, some are forced to detour round it. They converge again downwind, moulding the storm clouds into an ominous anvil-shape in the process. But while some wind goes round the mesocyclone, some runs full square into this meteorological brick wall and is forced downward, creating a "rear flank downdraught" (RFD) which many experts believe is what makes or breaks a tornadic storm.

It's when an RFD tries to swing around the base of the storm, narrowing the area of wind flowing into the updraught and increasing its spin (in the same way figure skaters when their arms are pulled in) that you might want to get into your getaway car. If you're anywhere beneath whirling piece of meteorological give and take—a funnel cloud—you are in a bad, dangerous place known to stormchasers as "the bear cage". It's where, if the funnel cloud sticks around long enough for the updraught to touchdown on terra firma, you will find yourself on the inside of a tornado.

Question:What can be inferred from the third paragraph

A. If an updraught is created, tornado appears.

B. A tornado comes into being when a RFD is created.

C. RFD is created if winds go round the mesocyclone.

D. When meeting supercell, winds will blow in all directions.