Preposition 1

We sit .........the dining table.

a) at

b) upon

c) on

d) by

 'by' is incorrect as it means 'sitting beside' the dining table for dinner. 'On' and 'upon' are incorrect as they mean sitting on top of the dining table for dinner. 'At' is used generally for indicating a specific location or place. So, the most appropriate answer is At.