When a system involving software is being developed, one or more cost models may be useful.
When a system involving software is being developed, there could be more than one model that is useful.
There is a system being developed but there only exists one cost model.
The Oklahoma horse mascot is surrounded by red fans.
It would have been better if you did not participate with us.
I am not sure; they are steadily declining.
a woman with a stroller gets a ball in the store
The island remained independent.
Water is not strong enough to collapse a tunnel.