Which is a complex sentence?

 - In June, Lexi and Todd will graduate with honors from Yardley High School.
 - Jonathan will lend us money for the tickets if we promise to repay him by the end of the year.
The second sentence is the complex sentence. It is made up of an independent clause and a dependent clause. The dependent clause begins with the subordinating conjunction if.
Jonathan will lend us money for the tickets if we promise to repay him by the end of the year.