Which statements about interstate compacts is true?

a. There are no compacts in effect among all 50 states

b. Congress generally must approve interstate compacts

c. The number of state compacts has declined since 1920

d. States cannot form compacts with foreign states

B. Congress generally must approve interstate compacts is the true statement regarding interstate compacts.

b. Congress generally must approve interstate compacts

Explanation:

An interstate compact is an agreement between two or more states, but in order for the compact to be in effect, it must be approved by the states' respective legislatures, and, then, generally, it must be approved by Congress. As Section 10, Article I, of the U. S. Constitution states:

No state shall, without the consent of Congress, lay any duty of tonnage, keep troops, or ships of war in time of peace, enter into any agreement or compact with another state, or with a foreign power, or engage in war, unless actually invaded, or in such imminent danger as will not admit of delay.