Answer:
a) After the unexpected & surprise attack of 9/11, there were consultations among the NATO allies & collective action was decided by the council. On September 13, 2001, the allies invoked the principle of Article 5 which states that if a Nato ally is the victim of an armed attack, each and every other member of the alliance will consider this act of violence as an armed attack against all members and will take the actions​ seems to be necessary against the attackers. Nato's main decision-making body agreed that if it is determined that the attack was directed from abroad against the United States, it would be regarded as an action covered by article 5. b) If we consider the core principle based on which NATO was formed i.e. the principle of collective defense that remains a unique principle that binds its all other members together, committing them to protect each other. In this respect we can assume that collective defense means an attack against one Ally is considered an attack against all Allies, NATO invoked Article 5 for the first time in its history after the 9/11 terrorist attacks against the United States​. So it is against terror attacks & against terrorist groups as well, so taking a such decision in such a crisis is appropriate. c) In order to take necessary measures to provide increased security facilities to the United States & to provide access to ports & airfields on the territory of NATO member countries for operations against terrorism it is essential to take collective responsibility to take such a huge task.
Step-by-step explanation: