Explanation:

- A Contingent contract depends on the occurrence or non-occurrence of a specific event. These contracts are conditional.

- A Quasi contract is an obligation imposed by law to prevent unjust enrichment. It's not based on party consent but is constructed by courts.

- An Expressed contract is formed by explicit written or spoken words. Parties clearly state terms and agreement.

- An Implied contract is created by actions or circumstances, rather than written or spoken terms.