Which of the following statements about pyelonephritis is incorrect?
选项：

A:Chronic pyelonephritis usually has an acute onset, and only localizing urinary tract signs.;
B:Acute pyelonephritis is a common suppurative inflammation of the kidney and is mostly caused by bacterial infection.;
C:The bacteria can enter into the urinary tract by ascending infection and haematogenous infection.;
D:Reflux nephropathy is the most common cause of chronic pyelonephritis.