Complex prepositions

I am writing in (a)   to your letter dated May 12.

In (a)   with tradition, everyone wore black.

Games are often canceled on (a)   of rain.

Let us briefly consider how you might analyze this claim by (a)   of the scientific method.

It’s better that we keep (a)   good terms with our neighbours.

With (a)   to your recent inquiry, I've enclosed a copy of our new brochure.

On (a)   of everyone here, may I wish you a very happy retirement.

Liz agreed to look after the baby in return (a)   a free room.

We’re collecting money in (a)   of cancer research.

I think they gave me the role (a)   of pity.