Why is the size of an empty class in C not zero

Question

Why does the following output 1?

#include <iostream>

class Test
{
};

int main()
{
    std::cout << sizeof(Test);
    return 0;
}

Answer 1

Since it would be conceivable for two different objects to have the same memory address, the standard forbids objects (and classes thereof) of size 0.

For this reason, classes of any size (at least 1) must exist, even if they are empty.