Biosynthesis of vitamin K (menaquinone) by spp. inhabiting the of humans is a potentially important mutualistic relationship for human health.

1. E.coli

2. Intestinal tract

Explanation:

E.coli bacteria are useful to humans when they live in the large intestine of humans. The large intestine is an important digestive structure as it is important for the reabsorption of the nutrients.

The E.coli living in the intestine use the available digested nutrients and synthesises the vitamin B and K which are absorbed and utilised by the human body.

Thus, E.coli and Intestinal tract is correct.

d. making up measurements to record.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.