Management has become more complex because

The correct answer is: B. the equipments used in many of the firm's activities have become more complex.

The equipments used in many of the firm's activities have become more complex, which has led to an increase in the complexity of management. This is because managers now need to have a greater understanding of the technology in order to make effective decisions. Additionally, the complexity of the equipment can make it difficult to coordinate and control the activities of the firm.

The other options are not correct because:

• Option A is not correct because there is no evidence to suggest that there is less time to react to competitive actions.
• Option C is not correct because both formal and informal communication are important for management, but they do not necessarily make management more complex.
• Option D is not correct because management is related to communication, as managers need to communicate with employees, customers, and other stakeholders.