Therank and filesoldiers showed remarkable courage and dedication on the battlefield. The underlined part refers to -

• The rank and file soldiers showed remarkable courage and dedication on the battlefield.

• Rank and file
English Meaning: the ordinary members of an organization as opposed to its leaders.
Bangla Meaning: সাধারণ স্তরের

Ex. Sentence: He is a rank-and-file soldier.
Bangla Meaning: সে একজন সাধারণ সৈন্য।

• অন্য অপশন গুলোর মধ্যে - 
• Hardworking - কঠোর পরিশ্রমী
• Courageous - সাহসী
• Extraordinary - অসাধারণ; সাধারণ নয় এমন বিশিষ্ট

Source: Website Lecture and Bangla Academy Dictionary.