Why did the building crew fill up tubs of water?

Calcium scale deposits occur when there's an excess of calcium in the water, also known as hard water. .

Explanation:

As calcium accumulates in the water over time, white flakes will start to form. Biofilm is made up of natural materials shed by those using the hot tub, which is an overgrowth of white water mold

the illustration   that would give a reader a clear understanding of the text is a picture of men constructing the frame of a building.the frame is made of iron bars. the text describes the job of blacksmiths'. these were very organised and they had different names: "the driver" and "the heater". the text describes the way in which these men worked ; they worked iron pieces as if they were playing a sport. in fact, the text wants to show the men's skills. the text also puts some emphasis on the use of '' rivets'' in construction. this kind of nails were not always used in the construction of manhattan.

some examples:

"and with an underhand toss he hurled the smoking rivet straight at the catcher, who caught it in mid-air in his catching can." men's skills

"when the driver was ready for a new " the emphasis on the rivet ( special nail used in construction).

" it against a beam to remove any cinders, and jammed it into the waiting hole. " the emphasis on the rivet.

the answer is not b, and i don't think its a, so i choose either man's identity is found within the traditions of his ancestors   or language is a powerful tool, tell me if i was wrong or right by the way