JuniorTheoryVery common

What happens when this program is compiled and run?

string cmd = "start";

switch (cmd)
{
    case "start":
        Console.Write("A");
    case "stop":
        Console.Write("B");
        break;
}

It does not compile

Expecting AB: in C# a case branch cannot run on into the next one, and a branch without break stops compilation with CS0163.
Expecting the compiler to add the break itself and print A: it adds nothing and reports an error instead.

How would you fix the program so that it prints A?
When may two case labels stand one under the other with no break between them?

JuniorTheoryVery common

string cmd = "start";

switch (cmd)
{
    case "start":
        Console.Write("A");
    case "stop":
        Console.Write("B");
        break;
}

It does not compile

Expecting AB: in C# a case branch cannot run on into the next one, and a branch without break stops compilation with CS0163.
Expecting the compiler to add the break itself and print A: it adds nothing and reports an error instead.

How would you fix the program so that it prints A?
When may two case labels stand one under the other with no break between them?