B4

Diamonds are a symbol of luxury for many people. People have valued diamonds as attractive jewellery for around 2,500 years.

(present perfect, т.к. событие продолжается до настоящего момента)

VALUE

B5

The Indians used them to decorate religious icons and it seems the ancient Chinese gave their axes a sharp edge using diamonds.

(past simple, т.к. речь идет об определённом времени в прошлом)

GIVE

B6 

Diamond is the hardest substance on Earth, meaning that only another diamond can be used to cut a diamond.

(Participle I, “имеется в виду”, подходит по смысловому контексту)

MEAN

B7

Diamonds consist of carbon and usually they are found deep underground in mines, but you might get lucky and see them on the surface.

(present simple passive, т.к. это общее утверждение)

FIND

B8

Mining companies in places like Africa make a lot of money from diamonds.

(мн.ч.)

COMPANY

B9

However, the miners themselves are often quite poor.

(сами)

THEY

B10

The value of a diamond is judged on four criteria, known as the four Cs: carat (or size), clarity, colour and cut.

(Participle II, “известные”, подходит по смысловому контексту)

KNOW

B11

The heaviest diamond ever found was the Cullinan diamond,which was discovered in 1905 and weighed 621 grammes.

(степень сравнения)

HEAVY