Which of these can be described as a system of stars, gases, dust, and other matter that orbits a common center of gravity? OPTIONS:
- an asteroid
- a galaxy
- a nebula
- a comet
A: a galaxy

Which part of an atom is involved in chemical reactions? OPTIONS:
- nucleus and its particles
- negatively-charged particles
- neutrally-charged particles
- positively-charged particles
A: negatively-charged particles

Which mineral has six-sided transparent crystals that will scratch glass? OPTIONS:
- sulfur
- quartz
- calcite
- feldspar
A: quartz

Which of these is most likely the cause of a father and son having almost identical-sounding voices? OPTIONS:
- learned behaviors
- environmental conditions
- inherited characteristics
- instinctive characteristics
A:
inherited characteristics