What type of consent is not effective in the context of A's entry onto B's land?

Consent given under duress is not effective in the context of A's entry onto B's land because it does not reflect the true and voluntary agreement of B. Duress involves coercion or threats that compromise the voluntary nature of consent, meaning that any agreement made under such conditions is void. For consent to be legally recognized, it must be given freely and without undue pressure or coercion.

In contrast, verbal consent, as long as it is given freely and willingly, can be effective. Consent implied by circumstances can also serve as valid consent if a reasonable person would interpret actions as consenting to the entry. Written consent is typically seen as a stronger form of agreement. Each of these options generally establishes the ability of A to enter B's land legally, while consent given under duress fails to meet the necessary legal standard.