You will be given a definition of a task first, then some input of the task.
In this task, you need to answer the given multiple-choice question on geometry. Classify your answers into 'a', 'b', 'c', 'd', and 'e'.

Problem: the slant height of a cone is 13 cm and radius of the base is 9 cm , find the curved surface of the cone ? 
Options: a ) 367 , b ) 378 , c ) 365 , d ) 26 , e ) 28
Output:
a