As shown in the picture, "A map of the near-surface weather situation in a certain area of China", read the picture to answer the following questions. (1) The pressure value of isobar C in the picture is _ _ _ _ _ (higher than or equal to.

(1) The frontal surface is located in the trough of low pressure, belonging to frontal cyclone, with the central air pressure lower than its surroundings, and the pressure value of isobar C is higher than that of D; On the isobar chart, the specific wind direction is from high pressure to low pressure, and the northern hemisphere deflects to the right. At this time, the wind direction in Chongqing is northwest wind (or northerly wind).

(2) It can be judged from the symbol of the front that the front is a cold front, and there will be strong winds, cooling, rainy weather and even snowfall when the cold front passes through the border.

(3) Compared with Chongqing, Changsha has stronger wind force and dense isobars. The horizontal pressure gradient force is great.

(4) The important role of rivers in the formation and development of Wuhan and Chongqing is to provide sufficient water resources and convenient water transportation.

(5) The reason why the A section of the middle and lower reaches of the Yangtze River has become an "overground river" is that it is located in the plain, the river channel is curved, the water flow is slow, a lot of sediment is deposited, and the riverbed is constantly silted up.

So the answer is:

(1) Dense isobars and large horizontal pressure gradient force?

(4) Providing sufficient water sources for water transportation

(5) Being located in the plain, the river course is curved, the water flow is slow, a large amount of sediment is deposited, and the riverbed is continuously silted up.