If the table shows the temperature observation records from 20 10 to 12 to 17 in Xuzhou, please answer questions 6-7. Date 12, 13, 14, 15, 16.

A.this picture is a high-voltage system. From the watch, the temperature has been falling, below 0 degrees. After the system transits, the temperature drops, so it is a cold front weather system, which does not meet the question.

B.this picture shows a low-pressure system. From the watch, the temperature has been falling, below 0 degrees. After the system transits, the temperature drops, so it is a cold front weather system, which does not meet the question.

C.this picture is a cold front system. From the watch, the temperature has been falling, below 0 degrees. After the system transits, the temperature drops, so it is a cold front weather system, so it is correct.

D. This picture is a warm front system. From the watch, the temperature has been falling, below 0 degrees. After the system transits, the temperature drops, so it is a cold front weather system, which does not meet the question.

So choose: C.