[tex]\text{If a, b, c, d,... is an arithmetic sequence, then}\ b-a=c-b=d-c\\\\\text{If a, b, c, d,... is a geometric sequence, then}\ \dfrac{b}{a}=\dfrac{c}{b}=\dfrac{d}{c}\\\\Sequence\ 1:-10,\ 20,\ -40,\ 80,\ ...\\\\20-(-10)=20+10=30\\-40-20=-60\\not\ arithmetic\\\\\dfrac{20}{-10}=-2\\\dfrac{-40}{20}=-2\\\dfrac{80}{-40}=-2\\It's\ a\ geometric\ sequence\\\\Sequence\ 2:15,\ -5,\ -25,\ -45,\ ...\\\\-5-15=-20\\-25-(-5)=-25+5=-20\\-45-(-25)=-45+25=-20\\It's\ an\ arithmetic\ sequence}[/tex]
[tex]\dfrac{-5}{15}=-\dfrac{1}{3}\\\dfrac{-25}{-5}=5\\not\ geometric\\\\\\Answer:\ \boxed{A.\text{Sequence 2 is arithmetic and Sequence 1 is geometric}}[/tex]
