All the reactions mentioned—mucus secretion, contraction of bronchial smooth muscle, and vascular leakage (swelling)—are involved in the early phase of an asthma attack.
The early phase of an asthma attack is characterized by a number of allergic reactions. These can include mucus secretion, which leads to airway blockage, and the contraction of bronchial smooth muscle, which further narrows the airways and inhibits airflow. Additionally, vascular leakage (swelling) occurs, causing airway edema and contributing to the difficulty in breathing that characterizes an asthma attack. Therefore, the answer to the question is 'a. All of these answers are correct'.