One thing at a time. 
One thing at a time.
Two things at a time.
Two men drive a truck to the dump.
First Class among letters, flats, and parcels each have different rates.
She's as smart as a steel trap.
And there is a significant discrepancy.
There is a giant hole in the floor of the office that leads to another dimension that this man is trying to avoid being sucked into.
Three people are playing with legos and a cushion.