Which of the following actions would invalidate a contract?

In the context of contract law, a valid contract must include specific elements, one of which is mutual agreement between the parties involved. If there is a lack of agreement, meaning that one party does not consent to the terms or there is confusion about the contract's stipulations, then the contract can be considered void or invalid. Therefore, a lack of agreement fundamentally undermines the essence of a contract, as contracts are based on the mutual consent of the parties to the terms laid out.

The presence of an attorney, while it can play a role in ensuring that the contract is executed properly and in accordance with the law, does not, by itself, invalidate a contract. Similarly, a signature by involved parties signifies that they agree to the terms, which supports the validity of the contract rather than invalidate it. Lastly, providing a written document is usually necessary for certain types of contracts, particularly those involving real estate, but having a written document doesn't inherently cause the contract to be invalid. Thus, without mutual agreement, the contract lacks one of its fundamental components, rendering it unenforceable.