Which one of these statements about NOPAC system is true?
A.The two northern routes R220 and R580 are used for westbound traffic
B.The three southern routes are used primarily for eastbound traffic except R591 or G344 may be used for aircraft crossing RJJJ/PAZA FIR boundary between 0000Z and 0600Z
C.R220,R580 and A590 are one-way routes, R591 and G344 are two-way routes
D.All above
正确答案是D