Europe’s many are widely used for transportation, leisure, and tourism.
a. coastlines
b. dikes
c. polders
d. canals

The answer is Canal. Canals are human-made channels for water movement, or to administration water transport vehicles. In the vernacular, both are alluded to as 'trenches', and as a rule, the built works will have a progression of dams and bolts that make territories of the low-speed current stream. These territories are alluded to as 'slack water levels', frequently just called 'levels'.

The canals were used for transportation, leisure and tourims in Europe. In places like Venice where gondolas are used for travel and tourism. While coastlines can be used for transportation not many can use these. A d ike is a long wall that is used to prevent flooding from the ocean, while a polder is a low-lying land proctected by d ikes.