The golden rules of contour lines include the following: contour lines never cross, the closer the contour lines, the steeper the slope, and tops of hills and mountains are marked with closed circles.

Astudent poured a solution of bromothymol blue indicator into three test tubes. then he placed an aquatic plant in two of the test tubes, as shown below. he placed a stopper on each test tube and placed them all in the dark for 24 hours. bromothymol blue turns from blue to yellow in the presence of co2