Please help soon!! Erwin Chargaff's work on the composition of nucleic acids began in 1944. His findings, which later became known as
Chargaff's rules, detail the specific pairings that occur in double-stranded DNA molecules.
According to one of Chargaff's rules, a section of DNA molecule that contains 50 base pairs and has 15 adenine
bases must also contain

a- 15 guanine bases

b- 15 cytosine bases

c- 15 thymine bases

d- 15 uracil bases

answer: the answer is b

d. groundwater flows through the subsoil and deposits minerals.

thats not a question

igneous rocks are formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks.  

the composition depends on the source magma. there are almost a thousand types of composition found till now.  

hope this