Because there are a lot of people living there.
a large territory in which several groups of people are ruled by a single leader or government
PBX is a Private Branch Exchange. It is a separate telephone exchange, to serve a large building or office. PABX is a private automatic branch exchange. Where you can contact individuals automatically within a building by direct dialing.
One single spawning can be as large as several thousand ova.
Several small volumes is more effective.
Your lungs provide a very large surface area for gas exchange.
Small organisms, like a amoeba's, have large surface area : volume ratios which means the exchange can take place by diffusion through the cell wall, the same as any other single celled organsism.
An American Express office can exchange your money. You can also exchange it at the main branch of a large bank.
why can small cells exchange substances more readily than large cells?
That depends on how large your telephone box is.
It depends on what kind you're referring to. It can range from a few cents for a .22 (although, it's unlikely that you will find single bullets for sale anywhere) up to several dollars for a large caliber bullet.
Just that there are a lot of birds. A large number will rarely fit into a single V formation. It splits up and several such groups form.
Talligator