Question

Astronauts have completed a major mission in space.It was ______a replacement of the fuel tank in one of the space station.

Answer 1

Answer :-
Concerning
***Concerning here means (about)***

Answer 2

Answer :

This question is based on prepositions.

Cambridge English Dictionary defines 'preposition' as 'in grammar, a word that is used before a noun, a noun phrase, or a pronoun, connecting it to another word.'

'Concerning' is a preposition, which according to the Collins English Dictionary, means 'You use concerning to indicate what a question or piece of information is about.'

So, the correct sentence is :

Astronauts have completed a major mission in space.It was concerning a replacement of the fuel tank in one of the space station.