What is the role of the opposition party in a democracy?Explain

What is the role of the opposition party in a democracy?

The opposition party plays a very important role in a democracy as
(i) It acts as pressure group.
(ii) It mobilises the government.
(iii) It keeps a check on the working of the ruling party.
(iv) It puts different views in the Parliament and criticise the government for its failures or wrong policies.