Since

1. Since the total cost of these inputs is fixed, the average cost, the cost per unit produced, falls as output increases.
   
2. She has been here since Monday.
   
3. Since considerable trouble and expense may be involved in changing prices, firms prefer to set and maintain a price for a given period.
   
4. Profitability is normally the primary objective of private sector producers, since unless the firm earns adequate profits it will not survive.
   
5. Since the prices of shares and government securities change from day to day, a seller might receive more or less than he or she paid for them.
   
6. Since last year several of these basic industries have experienced a serious decline in their home and overseas markets.
   
7. Since it came into being, the EEC has made substantial progress.
   
8. I have been waiting for you since 2 o'clock.

I have never been to France.

Have you ever been to London?

I haven't seen you for ages.

I haven't met him for a long time.

I haven't been to Moscow since last year.