In what two ways can the frog population be used to monitor the river's water quality? Please help asap

Three cards with holes are arranged in a straight line. a light is shined through the first card’s hole and travels through all three cards. what does this tell you about light rays? a) that light is reflected b) that light is refractive c) that light travels in a straight line d) that light does not travel in a straight line

What is the independent variable in this investigation? mass volume sample number substance density

  the mississippians were considered to be  horticulturalists, which means they were