in the 18th century和in 18th century有区别吗?

in the 18th century和in 18th century有区别吗?
一篇英语阅读里面第一句：when tea and coffee were first introduced to Europe in the 18th century，第一个问题是tea and coffee were first introduced to Europe in______A______
A 19th century
B 18th century
C in 1801
D 1921
只有in the 18th century=in 19th century时才能选择A啊
难道in the 18th century和in 19th century指的都是1801~1900？
那in 18th century指的就是1701~1800？