执行下面python代码后，输出的结果是？（ ）
def add(c):
d = c.append(40)
return d
a = [10, 20, 30]
b = add(a)
print(a, b)
[10, 20, 30] [10, 20, 30]
[10, 20, 30, 40] [10, 20, 30, 40]
[10, 20, 30] [10, 20, 30, 40]
[10, 20, 30, 40] None