Fill in the blanks with the correct form of the verbs: "People who (a) ___ most often and most gloriously in the pages of history (b) great conquerors and generals. Whereas, the people who really (c)

"...most often and most gloriously in the pages of history (b) ______ great conquerors and generals."
The subject "People who... appear..." is plural, and the sentence describes a general truth, so the present simple tense of "to be" is used.

"Whereas, the people who really (c) ______ civilization forward..."
The subject "people who" is plural, and the sentence describes a general truth, so the present simple tense is used.

"...are often never (d) ______ at all."
This part of the sentence is in the passive voice ("are never mentioned"), as the people are the recipients of the action of mentioning. The past participle form of the verb is needed.

"We do not know who first (e) ______ a broken leg..."
This refers to a past action by an unknown person. The past simple tense is used.

"...or (f) ______ a sea worthy boat..."
This is parallel to blank (e), referring to another past action by an unknown person. The past simple tense is used.

"...or (g) ______ the length of a year."
This is parallel to blanks (e) and (f), referring to another past action by an unknown person. The past simple tense is used.

"The great men are those who (h) ______ ceaselessly to quicken the pace of civilization."
The subject "those who" is plural, and the sentence describes a characteristic or ongoing action, so the present simple tense is used.

"On the contrary, the condemned men are those who (i) ______ bloodshed and violence in the world."
The subject "those who" is plural, and the sentence describes a general characteristic or action, so the present simple tense is used.

"We are highly indebted to those great men who contributed a lot to (j) ______ the civilization."
The phrase "contributed a lot to" is followed by a preposition "to", which typically takes a noun or a gerund (the -ing form of a verb acting as a noun).
j) flourishing

The completed text is:
"People who (a) appear most often and most gloriously in the pages of history (b) are great conquerors and generals. Whereas, the people who really (c) help civilization forward are often never (d) mentioned at all. We do not know who first (e) set a broken leg or (f) launched a sea worthy boat or (g) calculated the length of a year. The great men are those who (h) work ceaselessly to quicken the pace of civilization. On the contrary, the condemned men are those who (i) cause bloodshed and violence in the world. All of us praise the great men of the world. We are highly indebted to those great men who contributed a lot to (j) flourishing the civilization."