Find the topic sentence of the following paragraph. ( )

A、The Irish countryside is very beautiful.

B、There is a popular Irish song which says that there are 100 different shades of green in the Irish landscape, and this is no exaggeration.

C、Thanks to general rainfall, much of the countryside is covered in rich green vegetation, which is why Ireland is also known as the Emerald Isle.

D、It also has a varied landscape with dramatic mountains, rocky coastlines and rolling hills.

E、Thus, Ireland is one of the most appealing places for the tourists.