Apure substance made of only one kind of atom and cannot be broken down by chemical means. a. compound b. element c. mixture d. semiconductor

This is geometry. could anyone ? i can't fail this class. my grade is quite low already.

What could explain what happened when the time was equal to 120 minutes

Look at the figure below: triangle abc is a right triangle with angle abc equal to 90 degrees. the length of ac is 5 units and the length of ab is 4 units. d is a point above c. triangle adc is a right triangle with angle dac equal to 90 degrees and dc parallel to ab. what is the length, in units, of segment cd?