Study the images of two different fronts. Item A: Arrows for a cold front and warm front meet with high level, grey clouds. Item B: Arrows for a cold front and warm front are moving in the same direction. The warm front is above the cold front.

Based on arrow movement, why is the front shown in item A different from the front shown in item B?

Warm air rises above cold air in item A, while two air masses collide in item B.
Cold air mixes with warm air in item A, while two air masses barely move in item B.
Warm air is pushed upward near cold air in item A, while a boundary forms in item B.
Two air masses form a boundary in item A, while warm air rises above cold air in item B.

B

Explanation:

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).