Answer:
D) Exchange Rates: US$ and 41 Currencies
Step-by-step explanation:
This is because his research is based on historical facts .
By using all the other currencies rich is able to identifie the strennth of the currencies against each other.
The other reason is that the USD is the unit of measure on other currencies hence comparering it against other currencies then that of the pound makes it easier to identify how this currencies compare.