The phrase "a main activity" is correct and usable in written English.
It can be used to refer to the primary or most important task or action within a particular context or setting.
Example: "The main activity of the workshop will be hands-on training in digital marketing strategies."
Alternatives: "a primary task" or "a key activity".
Almost everyone imagines the diversion of government funds to be a main activity of the Russian banking system.
When you load up Gowalla, the first thing you see is still a main activity feed.
Task scheduling is a main activity in the design of real-time systems (RTS).
The main idea of our encoding is to ensure sensitivity for a main activity profile while penalizing deviations from the desired activity profile.
Here we identified a main activity component (Actmain), which seems unaffected by the work for food protocol, and a less intense activity component (Actshifted) that followed the main activity component under high reward ratio and ad libitum conditions.
Trying to prevent, control, and curb the growth trend of CDs in rural areas is a main activity of the Ministry of Health of China.
The story, rendered in an open-ended, sometimes confusing fashion, with little time wasted on exposition, is of a few days in the life of Moshe (Moshe Ivgi), a man whose main activity seems to be the cultivation of anxiety and neurosis.
Yet as a couple our main activity, it seemed, was making each other miserable.
When I was a kid, the main activity was to go up and throw rocks at the whores, bang on the doors, and have the pimps chase us down the Street.
3 Each session follows a theme or main activity (eg, current affairs, my life, word games) and is run by two facilitators.
As an adult, her main activity was swimming, which she did only in the summers and only because she spent a lot of time at a pool with her six daughters.
