Read these sentences from the section "Wild west". Yet, these barriers have their advantages, too. Chinese governments from the earliest dynasties have been forced to focus internally. Instead of trying to expand the country through conquest, China has focused on cultural and ethnic integration. Which word from the sentences helps you understand that barriers caused the people of China to become unified?

Cultural and ethnic integration.

Explanation:

Cultural integration is a process of cultural exchange which results in groups of people assuming and practicing the beliefs of other culture without sacrificing her own cultural attributes.

Ethnic integration involves social process by which different ethnics continue to interact resulting in ethnic identity of the participants.

China has about 56 ethnic tribes with about 55 minorities and 1 major tribe.

In the question, expansion through conquest is not the major concern of the Chinese governments but rather intergration of various ethnic and cultural  groups within its territories.

giant impact theory - the moon was formed from the collision between earth and another mars-sized body.

colliding planetesimals hypothesis - the moon was formed from the same cloud of material as earth.

capture hypothesis - the moon was locked into orbit by earths gravity as it was passing by it.

accretion hypothesis - the moon was formed from collisions and combining of planetesimals.

i think this is right, if not and you know better let me know.