which, that, what; should be, ma

which, that, what; should be, may be, shall be
It is said ______all cars coming from other cities ______performed quarantine.
【正确答案】：that/ should be
【题目解析】：It is said + that从句是固定用法，该句型是含有that从句的一种复合句，主语为形式主语it，意为“据说……”。