$11.$ I thanked the woman who had helped me. 

$12.$ The man who I respect his opinion most is my father.

$13.$ Tom has three sisters who are all.

$14.$ The doctor who you invited yesterday is famous.

$15.$ The taxi driver who took me to the airport is friendly.

$16.$ Phuong Thao is a singer who you like her music best.

$17.$ We visited people who were very nice yesterday.

- "who": là đại từ quan hệ thay thế cho người ở vị trí chủ ngữ.

$18.$ The man whose wallet was stolen called the police.

- "whose": là đại từ quan hệ chỉ sự sở hữu.

$19.$ I saw a lot of people and horses that went to the market.

- "that": là trạng từ quan hệ thay thế cho người, vật, đồ vật, con vật.

$20.$ He introduced me to his student most of whom were from abroad.

- "whom": là đại từ quan hệ thay thế cho người ở vị trí tân ngữ.