Question

_ teacher told me to do _ sun on _ blackboard fill the article​

Answer 1

Prepositions are words that indicate relationships with the other words in the sentence. Prepositions of place are used to refer to a place, usually to denote the location of something or someone.
Let's look at the usage of various alternatives in the option as preposition of place:
at : to refer to an exact place where something is situated / event
on : to refer to placement of something attached / adjacent to something else; to refer to something displayed on something else
in : means "inside"
of : not used as a preposition of place

In the sentence, as a reference to a specific location , i.e. the board. Therefore, the suitable preposition here is "at".

Thus, the correct complete sentence is:
The teacher is standing AT the board

Answer 2

Answer:

The teacher told me to do the sum on the blackboard