We can approximate the real return on an investment by subtracting the inflation rate from the nominal return on the inv

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We can approximate the real return on an investment by
subtracting the inflation rate from the nominal return on the
investment. For example, an investment that returns 10% per year
while inflation is 4% per year has a real (inflation adjusted)
return of approximately 6%. Which of the following outcomes is NOT
possible?

Nominal return is negative, real return is positive
Nominal and real returns are positive
Nominal return is positive, real return is negative
all of these outcomes are possible
Please explain why the answer is "all of these outcomes are
possible?