Which of the following statements is CORRECT?

A$.$

Foreign exchange dealers earn a profit by bringing together buyers and sellers of foreign currencies and earning a commission on each sale and purchase.

B$.$

Speculators earn a profit by a bid$-$ask spread on currencies they purchase and sell.

C$.$

Currency trading lacks profitability for large commercial and investment banks but is maintained as a service for corporate and institutional customers.

D$.$

Arbitragers seek to profit from simultaneous exchange rate differences in different markets.