Many reactions take place in the blast furnace simultaneously.

Solution (By Examveda Team)

Simultaneously : at the same time.
Invariably : in every case or on every occasion; always.
Contemporarily : existing, occurring, or living at the same time; belonging to the same time.
Separately : as a separate entity or entities; not together.
Momentarily : for a very short time.

Antonym of Simultaneously is Separately