The dna consists of
a. four strands
b. one strand
c. three strands
d. two strands

The correct answer is option D. two strands.

Explanation:

DNA is a genetic molecule that is a basic unit that carries the genetic information for functional, developmental, growth and reproduction of all organisms and many viruses.

DNA has two complementary strands that make a double-stranded segment of DNA that coiled and antiparallel to one another. The antiparallel strands are run in opposite directions to each other but physically parallel. These strands are made up of nucleotide and called polynucleotides. This nucleotide consists of one of four nitrogen bases, a deoxyribose pentose sugar, and a phosphate group.

Thus, the correct answer is option D. two strands.

c. is the correct answer

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.