若有以下程序：
#include＜iostream＞
using namespace std；
class Base

public：
Base()

x=O；

int x；
；
Class Derived1：virtual public Base

public：
Derived1()

x=10；

；
class Derived2：Virtual public Base

public：
Derived2()

x=20；

；
class Derived：public Derived1，protected DeriVed2
；
int main()

Derived obj；
cout＜＜Obj.x＜＜end1；
return 0；

该程序运行后的输出结果是

A．10

B．20

C．30

D．0

Without the friction between their feet and the ground, people would () be able to walk.

A. in no time

B. by all means

C. in no way

D. on any account