B7

The Great Wall of China runs for 6,700 kilometers from east to west of China. It is one of the greatest wonders of the world.
(степень сравнения

 GREAT

B8

The Great Wall was built in order to protect the country form different aggressors.
(past simple passive, т.к. стена была построена, а не сама построила что-то)

BUILD

B9

The construction of the Wall began in the 6^th century BC and lasted until the 16^th century AD.
(past simple, т.к. действие произошло в определённый момент в прошлом)

BEGIN

B10

Since then, the Great Wall of China has become a Symbol of wisdom and bravery of the Chinese people and a monument to Chinese nation for many hundreds of years.
(present perfect, т.к. действие началось в прошлом и продолжается до сих пор)

BECOME