The correct answer is A. Flexible.
Resilient means able to recover quickly from difficulties; strong in the face of adversity.
Flexible means able to bend easily without breaking.
Proud means having or showing a high or excessively high opinion of oneself.
Separable means able to be separated or divided.
Rigid means not easily bent or changed.
A flexible person is able to adapt to change and cope with difficult situations. A proud person is confident and self-assured, but may also be arrogant and dismissive of others. A separable object can be divided into two or more parts. A rigid object is not easily bent or changed.
In the context of the question, the correct answer is A. Flexible. A resilient person is able to bounce back from difficulties, and this is often because they are flexible and adaptable.