television is one of the great advances in methods of communication that___ made in the 19th century

题目

television is one of the great advances in methods of communication that___ made in the 19th century
A was B were
请问
1 that 这里指什么
2 如果按照句意,感觉说的应该是television was made in the 19th century.
这句话如何分析用复数呢?

答案

that指的是advances,所以谓语动词自然是复数.