Generally, contract language such as if, on condition that, provided that, when, after, and as soon as indicates a(n) a. license b. covenant c. allonge d. easement e. condition

I believe the answer is: E. condition.

In a contract, condition refers to the obligations that each parties in the contract have to fulfilled within a specific time period.
If there is even a tiny part of the obligations are not fulfilled by one party, the other party have the right to void their obligations in the contract and even has the right to sue to party that void them.

D. providing for public safety