The correct answer in A is structurally equivalent to B

can someone help me explain why C is NOT structurally equivalent to D?

and what is the meaning of Bw? is it a function of B with w as an input or concatenation?

Many thanks

please answer the following questions i will surely upvote with many accounts and please answer fast

Consider the following declarations in C syntax (the code is not C code though) struct A{ int x; struct By;} struct B{ int x; struct Ay;} struct C{ int z; struct Bw;} struct D{ int d; struct Ae;} We consider the definition of structural equivalence used in the OCaml language. Which of the following is true (more than one answer can be correct)? A is structurally equivalent to B A is structurally equivalent to C B is structurally equivalent to C C is structurally equivalent to D