Can i say this sentence, is this sentence grammatically correct. can i add it in my essay?

the sentence is:

after 4 years, a coincidence no one ever thought would happen, happened.

What task did the surveyors do? a. they studied the landscape to determine the most direct route for building a road. b. they designed treadmills that lifted blocks of stone to where they were needed. c. they dug trenches and filled them with sand, concrete, and large blocks to form a road.