Brón orm arís!
Beidh mé an-bhuíoch as éinne a bheadh sásta cabhrú liomsa:


Aimsir brea nó aimsir bheara agus cén fáth leis sin?
Obair dian nó obair dhian

trasna an urláir- sin ceart?
Ag déanamh an obair nó ag déanamh na hoibre? Cén fáth?

Dhúnadar- sin an aimsir chaite? Nach é?

I myself would say:

obair dhian
aimsir bhreá

for the simple reason that "obair" and "aimsir" are feminine. I recall however some sort of intracie about whether people say "obair baile" or "obair bhaile"... I don't remember the particulars.

"trasna an urláir" is what I'd say.
"ag déanamh na hoibre" is what I'd say.

"dhúnadar" = "dhún siad".

Féach ar seo:

http://www.nualeargais.ie/gnag/gram.htm

agus seo:

http://www.nualeargais.ie/gnag/gram.htm

Chan fhaca mé 'n suíomh sin go fóill. Tá sé thaire bheith maith! Comhghairdeachas, a Lars !

Má bhíonn guta i gceist agus má bhíonn baininscneach nó firinscneach-cad a tharlaíonn?
an obair dian nó an obair dhian?
an t-eolas maith nó an t-eolas mhaith

The rule doesn't change, regardless of whether the noun begins with a vowel:

an t-eolas maith
ag lorg an eolais mhaith

an obair dhian
ag déanamh na hoibre déine

Here's ways we remembered it at school:

A man wears a tie: an t-eolas (masculine)
A woman wears a tie sometimes: an tsráid (feminine)

When you're dealing with the genitive, just reverse the rules! Where the was no séimhiú, put a séimhiú. Where there was a séimhiú, remove it.