in 18th century 要不要加the变成in the 18th century

Realistic novel in the 18th century Europe in the 18th century是什么意思 初中英语in the 18th and 19th century in the 18th century和in 18th century有区别吗? in the 16th century什么意思 in the 20th century是什么意思 在19世纪,翻译成英语in 19th century中间要加the吗? 英语单项选择 急1.In the 18th century writers__hours in coffee hours 7In the 18th century writers___hours in coffee houses,discus 9.The story is the 18th century in Canada.（ ） 想要知道翻译 since the founding of Taipei in the 18th century, in the 20th century,in the 1950s,这两个时间词的前面为什么要加 the?