The underlined word in the sentence is "march." To find the correct antonym, let's analyse the options:

1. Strut – To walk in a proud or stiff manner (Not an antonym).

2. Amble – To walk at a slow, relaxed pace (Possible antonym).

3. Trudge – To walk slowly with heavy steps, often due to exhaustion (Not an antonym).

4. Ramble – To walk aimlessly without direction (Possible antonym).

Since "march" means to walk in a steady, rhythmic, and purposeful manner, the best antonym is "amble" (B), which means to walk slowly and without urgency.