after he had (ran,run)about 5 kilo, he had (sank,sunk) to the ground

Answer 1

You are working with the Past Perfect verb tense in that sentence. Check the
site below.

http://www.englishpage.com/verbpage/pastperfect.html

This site will give you a summary of all forms of verb tenses.

http://leo.stcloudstate.edu/grammar/tenses.html