The iron with which they make the houses or bridges is the same as our blood?

Explanation:

yes, they are the same.

"Iron is a mineral that the body needs for growth and development. Your body uses iron to make hemoglobin, a protein in red blood cells that carries oxygen from the lungs to all parts of the body, and myoglobin, a protein that provides oxygen to muscles."

Fun fact:

At 4 grams per person, you'd need at least 2,352 completely drained donors to make a iron longsword out of blood.

its first and third is your answer i did the qustion the fourth isnt right