There would have to be a long period of chronic symptoms which would at once have attracted my attention. 
There would have been symptoms for a long time.
There would have been symptoms for just a short time..
A girl is playing basketball outside.
The people are by water.
People listening in a conference room
Is said that the cannon is able to bestow, that's why there are flowers in the barrel.
The band's performance was cancelled.
they have never said that before.