Read the following Python code carefully and point out the global variables?

y, z = 1, 2
def f():
    global x
    x = y+z

A. It specifies the value to be returned from the function B. It ends the execution of the function C. It prints the result on the screen D. It defines the function's name

A. By using the optional keyword B. By providing a default value to the parameter C. By making the parameter lowercase D. By using a special keyword opt

A. my_function B. 2nd_function C. _function D. function123

A. It is used to define a function B. It is used to declare a variable C. It is used to import a module D. It is used to create a loop