@WW just to be clear: B or C is not something I would choose to teach; (just grabbed the workbook to cover someone's class.) I think textbooks like to be seen to "cover" every possiblity. I doubt Englsh learners need to be able to produce C, when A and D are quite good enough.

@WW A and D are both fine and normal; there's no issue about that.
Context? well I think not.

@WW cf New Headway Intermediate workbook Unit 4 section 2 Item 9 : answer is given as "will we have to" : why can't we say 'shall we have to' - "because people don't" - and so on...

@WW I really don't have any special knowledge of ME or OE, just what I have gleaned from the web in dealing with "the Anglish question", which made me broaden my scant understanding. There is much more info on the web than was wonted several years ago, and I managed to plow thru David Cargill's book. The upshot is somewhat unsettling: for instance, years ago I would have marked "with hearty greetings" at the end of a letter as outright wrong (being copied from German) but now I know it was used in English certainly as late as the fifteenth yearhundred, I am not so black-and-white about things, (outside of exam purposes) .

@WW I would agree.

That's from 1913

@HS Perhaps "The Vocational Guidance Quarterly" vol 32 p196 would serve:
"Encourage the mentee to approach life and goals with enthusiasm"

@WW I must own up, all these years so focussed on when to use an article or not, i've never bothered much with the pron thereof. I often have heftier matters on my mind, like struggling with the audiobook of Zhivago and thinking that Pasternak's characterization of women really doesn't stack up, although I can't find a forum where this is discussed.:{

@WW Troilius and Cressida : Oon ere it herde, at tothir out it wente" Book 4, line 434.
The parsons tale: Of worldly shame? certes, an horrible homicide
The Knight's Tale : With bowe in honde, right as an hunteresse
My take on "a" is that it is a weak form of "an" (one), so the pron just varies over time and place. Much the same as "the" is by word-roots just a "weak" form of "this/that" as they all stem from the same roots, and again in today's English the pron is much a matter of upbringing and taste.

As 'a' is but a short form of 'an', itself a variant of 'one', and all one and the same in OE/ME it may not be worthwhile starting WWIII over this.