Taiwan is the largest island in our country.It is —the east

选B
on、at、in还可以表示两地相对位置.
若A地属于B地,用in;
A地位于B地的外面且有边缘衔接用on；
无边缘的衔接有to.如：
Japan lies to the east of China.(范围之外)
Taiwan lies in the southeast of China.（范围之外）
Hunan province lies on the west of Hubei province.(毗邻)
The island lies off the coast of China.(相隔一定距离)
希望有所帮助.