You want to test the effect of soil acidity on plant growth. Which of the following is an example of a controlled experiment to test this?
O A. The soil acidity of plants in a garden that get light and water from
their surroundings is increased after the plants grow to a height of
100 cm.
O B. Soil acidity and height of plants growing in a 10 m2 yard are
measured twice in July and twice in August.
c. The plant type, amount of light, and amount of water are kept
constant while soil acidity is varied for plants in a greenhouse.
OD. The plant type, soil acidity, amount of light, and amount of wnter
are all varied and studied in a laboratory.

aquifers are bounded above and below by impermeable rock. the driving force of groundwater movement in confined aquifers is pressure, rather than gravity.

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).