7th grade science pls help

In dna, only the_ varies from one nucleotide to another. base phosphate sugar amino acid

Which set of characteristics best describes sedimentary rock? a) largest type of rock, made of organic matter, hardest type of rock b) often contains layers, forms near sources of water, contains fossils c) least abundant type of rock, made of other rocks, made mostly of minerals d) most abundant type in earth's crust, made of magma/lava, contains no fossils

What is the cause hearing loss in human being