D is the abbreviation of did, had or would. If it is followed by the verb prototype, it is the abbreviation of did; If it is followed by a past participle or "better+prototype", it is the abbreviation of had; If it is followed by "would rather/like to+prototype", it is the abbreviation of would. For example:

Where did you go yesterday? Where were you yesterday? = Where is it

He's gone. ? He has already left. he has

You'd better go away. ? You'd better go away. you have

I would rather walk than drive. = I will

I want to go. I want to go. = I will