Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) What I need to know about Erectile Dysfunction ?
    ### Response:
    Erectile dysfunction* is when you cannot get or keep an erection firm enough to have sex. You may have ED if you
                
- can get an erection sometimes, though not every time  - can get an erection, yet it does not last long enough for sex  - are unable to get an erection at all

    