Questions

Yes, a promise can be broken without being held.

A restrictive clause is one that limits the meaning of the word it describes.

For example :: 

The girl who lives next door is beautiful.

This restrictive clause limits "the girl" to say it's specifically the one next door.

In 1975, a party called khmer Rouge had taken control of Cambodia under the leader ship of Pol Pot. The Government of Pol pot established a regime of terror in Cambodia and started following a policy of genocide against its own people.

Arunachal Pradesh State has been declared as the Open Defecation Free state.

Income easticity of demand measures the responsiveness of demand for any goods to changes in income. With increase in incomes generally the demand for farm products like rice wheat etc, will not change drastically. With income increase, demand for luxuries such as consumer durables etc will increase. The income elasticity  of demand for farm products is thus low.