For Ethel to claim easement by prescription, how many years must she have crossed Terry's property?

To claim an easement by prescription in Arizona, a party must demonstrate that the use of another's property has been continuous, open, and notorious for a statutory period. In Arizona, this statutory period is 10 years. Thus, for Ethel to successfully claim an easement by prescription over Terry's property, she must have been using the property in a manner that meets these criteria for at least 10 years. This requirement ensures that landowners have a clear chance to observe and address any unauthorized use of their property over a substantial amount of time.

Using the other options as a reference, a shorter period such as 5 years would not meet the legal criteria for prescription claims, while longer periods such as 15 or 20 years exceed what is required by Arizona law, making them unnecessary for Ethel's claim.