class A; class B { A *m_a; public:B(A *a) :m_a(a) { } }; class A { A() :b(this) { } B b; };这段代码中A() :b(this)这句话不是对成员变量b进行初始化吗 但是在B类中没有无参数的构造函数 这段代码 我看不懂

We are in____ a.one class b.class one c.Class One d.Class one We are in____ .a.one class b.Class First c.Class One d.Class one what class are you in? 回答（ ） A：class B：class three C：Class Three D：Class three public class test(){ public Class a(int i) {} public static class b{} }public class test(){public Class a(int i) {}public static class b{}} They are having ---A,a class B,English class.C,Chinese class请问选哪一个 判断 we are in（） A ,Class three B,class 3 C,Class Three It time for ____. a,clsss b ,have class,c,to class,d,has class Don't talk loudly here.The students_____.A.have class B.are having class C.class D.are have class After() class,they often play soccer.A.having B.the class C.have class D.class over顺便讲讲道理, Is your brother in ____?A.Class three B.Class Three C.class five D.class Five Mary and her brother are in ___.A.class one B.Class One C.one class D.One Class have a class是什么意思 have a class meeting have a class party give you a class CLASS：A怎么翻译 on a first-class a world class photographer