帕金森病引起强直、震颤等症状的原因是A．黑质-纹状体多巴胺能神经功能减弱 B．纹状体

30°15′=（    ）°。

No one but the experts in this field can _____ the difference between them.

A．recognize

B．speak

C．spot

D．predict

有如下程序：
#include ＜iostream＞
using namespace std;
class point int x, y;
public:
point( int vx, int vy )

x = vx;
y = vy;

point ( )
x = 0;
y= 0;

point operator+( point p1 )

point p;
int px = x+ p1.x;
int py = y + p1.y;
return point( px, py );
point operator-( point p1 )

point p;
int px = x -p1.x;
int py = y - p1.y;
return point ( px, py );

void print()

cout＜＜x＜＜" , "＜＜y＜＜end1;

;
int main () point p1(10, 10 ), p2( 20, 20 );
p1 = p1 - p2;
p1.print ();
return 0; 执行后的输出结果是

A．10，10

B．20，20

C．10，20

D．30，30

喷吹燃料后高炉冶炼特点是什么？