A. their B. whose C. which D. that
选A。因为句中有并列连词and，整个句子为并列句。
(3) On Sundays there were a lot of children playing in the park, _______ parents sitting together joking.
A. their B. whose C. which D. that
选A。their parents sitting together joking 为独立主格结构。
(4) On Sundays there were a lot of children playing in the park, _______ parents sat together joking.
A. their B. whose C. which D. that
选B。whose parents sat together joking 为非限制性定语从句，因为句中有完整的谓语 sat。
(5) On Sundays there were a lot of children playing in the park, _______ parents were sitting together joking.
A. their B. whose C. which D. that
选B。whose parents were sitting together joking 为非限制性定语从句，因为句中有完整的谓语 were sitting。
9、 If the man is only interested in your looks, _____ just shows how shallow he is.
A. as B. which C. what D. that
【易错】容易误选A或B，误这是非限制性定语从句。
【分析】正确答案为D，注意逗号前是一个条件状语从句，逗号后是该状语从句的主句，that 在此代表前文所述的情况，用作主句的主语。类似地，下面几道题也选 that，而不选 which：
(1) If you promise to go with us, _____ will be OK.
A. as B. which C. and it D. that
(2) If you want a double room, _____ will cost another ￡15.
A. as B. which C. what D. that
(3) Whether you go or not, _______ is quite all right with me.
A. that B. which C. and it D. so
(4) When I say two hours, _____ includes time for eating.
A. as B. which C. what D. that
9、 She says that she’ll never forget the time ________ she’s spent working as a secretary in our company.
A. which B. when C. how D. where
【易错】容易误选B，机械地认为时间名词后必须用关系副词when，地点名词后用关系副词 where。
【分析】正确答案为A。在时间名词和地点名词后是否用关系副词要看它在定语从句中充当什么句子成分。一般说来，若用作主语或宾语，用关系代词;若用作状语，则用关系副词。上面一题中的动词 spent 缺宾语，故应用关系代词 which或that。比较下面一题，由于空格后的句子不缺少主语或宾语，所以选关系副词when：
She says that she’ll never forget the time ________ she works as a secretary in our company.
A. which B. when C. how D. where
请再做一组试题(答案均选A)：
(1) Our company will move to a tall building _______ we bought last month.
A. which B. when C. how D. where
选A，which 在定语从句中用作动词 bought 的宾语。
(2) Our company will move to a tall building _______ has just been complete.
A. which B. when C. how D. where
选A，which 在定语从句中用作主语。
(3) Our company will move to a tall building _______ we worked two years ago.
A. where B. when C. that D. which
选A，where 在定语从句中用作状语。