考虑如下的定义类时，类之间的多继承关系，要求：(1)根据类定义的关系画出继承关系图；(2)类D的mro属性值是多少？ >>>class A1: pass >>>class A2: pass >>>class A3: pass >>>class B1(A1,A2): pass >>>class B2(A2,A3): pass >>>class B3(A3): pass >>>class C1(B1): pass >>>class C2(B1,B2)： pass >>>class C3(B2,B3): pass >>>class D(C1,C2,C3): pass

继承关系图如下：

     A1     A2     A3
      \     |     /
       \    |    /
        \   |   /
         \  |  /
          \ | /
           \|/
            B1
           / | \
          /  |  \
         /   |   \
        /    |    \
       /     |     \
      C1    B2     C3
       \   / \   /
        \ /   \ /
        C2    B3
         \   /
          \ /
           D

类D的mro属性值是：D -> C1 -> B1 -> C2 -> B2 -> C3 -> B3 -> A3 -> A2 -> A1 -> object