To trade stocks in a stock market is called all of these EXCEPT
A. exchange
B. buy/sell
C. trade
D. open market

open market

Step-by-step explanation:

1. Open market is form of market where entry and exit of traders are open to all. Anyone who wishes to do business in such market can do so freely without being charged for selling.

2. If one wishes to buy stock through stockbroker, one can place an order which is market order. In such process if one wishes to buy stock, he has to give ask price (willingness to pay for a stock)

If one wishes to sell his stock, he has to give bid price (amount for which one is willing to sell his stock)

This process is called buy/sell

3. Stock exchange is the place where exchange of stock is done. In exchange share of public company are transacted at stock exchange.

4.Trade mean transferring the ownership of stock to seller from buyer in exchange of money. Both buyer and seller must agree on a specific price.

Hence based on above definition we can see that open market does not qualify for definition of trade stock while others are  difference form trading in stock market and hence open market is correct answer for the question.