A:as twice many machine
B:twice many as machine
C:as many machines twice
D:twice as many machine
珠江三角洲是著名的____ ,为吸引外来____ ,尤其是____ 提供了有利条件。
下图是北半球局部图,AD、BC为纬线,且BC弧度为90°,AC为晨昏线且与纬线相切于C点,图示区域恰好为7日。读图回答下列各题。