New words：

tributary [ˈtrɪbjəˌteri]
adj.纳贡的；从属的；支流的
n.支流

Sample Sentences：

The Weihe River is the largest tributary to the Yellow River.

Looking at the map, it does seem like Korea has always been a tributary to China.

New words：

tribute [ˈtrɪbjut] n.贡品；贡物；致敬；（表示敬意的）礼物，颂辞，行为

pay tribute to 进贡；表示敬意；称赞；致敬

Sample Sentences：

The song is a tribute to Chairman Mao.
The doctor paid tribute to his nurses by praising their work.
The small kingdoms had to pay tribute to the big kingdoms in acient times .

New words：

tribe [traɪb] n.部落

Sample Sentences：

None of the tribes speak the same tongue.
Primitive tribes lived by fishing, hunting and gathering.
The village tribe is friendly and they share their water supply with you.

primitive [ˈprɪmətɪv] adj.原始的；远古的；发展水平低的；落后的

New words：

reproof [rɪˈpruf] n.责备；谴责

Sample Sentences：

Miss Liu looked at me with reproof.
His words were a mixture of pity and reproof.
He picked up the broken vase without a word of reproof to this son.

New words：

mild [maɪld] adj.温和的；和善的；不严厉的；和煦的

Sample Sentences：

It's been a very mild winter this year.
She received a mild reproof from the teacher.
If you prefer mild flavours reduce or leave out the chilli.

reproof [rɪˈpruf] n.责备；谴责