What can be concluded about A's action of presenting the written consent if it was obtained under duress?

In situations where consent is given under duress, the validity of that consent is compromised. Duress involves coercive pressure that nullifies the voluntary nature of the consent, meaning A's written consent does not hold legal weight. Therefore, the custodian of B has a responsibility to ensure that only valid consent is honored. If the consent was obtained through coercion, B’s custodian would be obligated to deny entry to A, as allowing entry would violate the principles of protecting individual rights against non-consensual actions.

The other options do not reflect the implications of duress accurately. Written consent obtained under duress cannot be considered legitimate, as it fails to meet the requirement of voluntary agreement. A's ability to pursue further legal action could be contingent on various factors, but it is not the immediate conclusion that arises from the situation of duress and consent. The notion that A must vacate the area immediately does not directly address the implications of the duress involved in obtaining consent. Instead, it’s the custodian's role to deny entry until a clear and valid consent is presented.