Complex prepositions

I am writing in _________________ to your letter dated May 12.

In __________________ with tradition, everyone wore black.

Games are often canceled on _______________ of rain.

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

It’s better that we keep _______ good terms with our neighbours.

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

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

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

We’re collecting money in ___________ of cancer research.

I think they gave me the role ____________ of pity.