There are many factors involved in the improvement in the life expectancy such as sanitation, housing, scientific research to cure many diseases and infections, education etc.
Historically it was the nineteenth and early twentieth century when all these improvements were made due to which the mortality rate decreased intensively in early and middle ages.
The verb here is "had given"; this is past perfect: it's a perfect tense, because it has a past participle with the -ed ending ("given") and it's the past perfect because the auxiliary verb is the past form of "have": had.
C. He goes for a walk near Jack's group.
