If the U. S dollar is strengthening, then:

a. it has been unpegged from other currencies.
b. the U. S has adopted a hard peg policy.
c. the U. S has purchasing power parity.
d. it has appreciated in terms of other currencies.

d.it has appreciated in terms of other currencies.

Explanation:

Currency appreciation occurs when the value of a currency increases. It leads to increase in demand of the currency against another currency as currencies are traded in pairs or against another currency.Appreciation of currency is caused by a number of factors such as investments, trade, economic policies, businesses, trad balance, etc.If the U.S dollar is strengthening then the currency of U.S has appreciated against other currencies.

Earthquake fault lines. map above represent