Econ Market Failure T/F Questions?

1. Market Failure occurs when positive externalities are present, but not when negative externalities are present.
2. Government sometimes intervenes when market failure occurs.
3. Market failure occurs when negative externalities are present, but not when positive externalities are present.
4. Market failure occurs when either negative or positive externalities are present.
5. Market failure is when market provision of a good results in an inefficient quantity.
6. Externalities are the only example of market failure.

I know for sure #6 is False, but the rest, I'm having so much trouble with. I had the homework problem wrong 4+ times because it is not telling me which part of the question I'm having wrong.