Below you will find useful information to understand how the EE is assessed. Remember, the EE is a requirement to obtain the IB diploma, but a D will yield zero points for you. The grade of the EE is combined with the grade of TOK to give you points towards your IBDP, but failing any of them will be considered failure of the whole program. If you want to know more, check page 97 of the EE Guide.
Consider the document below to help you with Criterion D, Presentation.