Reduce number of conditions

I have this long list of conditions inside a function:

if x == "a":
    return function_a()
elif "b" in x:
    return function_b()
elif x == "c string":
    return function_c()
elif x == "d string":
    return function_d()
else:
    function_e()

How can I simplify this so that I can reduce the cognitive complexity of my function?