Abnormal attitude law is caused by:

Abnormal attitude law is specifically triggered by an airplane entering an upset condition, which means it has reached an extreme attitude that goes beyond the normal operational limits. This condition can arise due to factors such as excessive pitch or bank angles, which can occur during unusual flight maneuvers or loss of control situations.

In contrast, the other options refer to different scenarios. Multiple failures of redundant systems or a triple ADR failure denote breakdowns in flight control systems but do not directly cause the conditions that lead to abnormal attitude law. Exceeding high-speed protection pertains to limitations related to speed rather than pitch or roll attitudes, and while these conditions could influence the flight characteristics, they do not specifically lead to entering an abnormal attitude. Hence, the correct answer is rooted in the aircraft's physical position and orientation in the event of an upset, necessitating the transition to abnormal attitude law for recovery.