225- Insects are regarded as valuable in biology because ................. .
A) scientists have grown used to working with them
B) they enlighten many dark sides in this field
C) they have many similarities with mankind
D) people consider them to be good-natured
E) of their low cost and simplicity
Mars is the fourth planet in order of distance from the Sun and seventh in order of diminishing size
and mass. It orbits the Sun once in 687 Earth days and spins on its axis once every 24 hours and 37
minutes. Owing to the relatively large irregularity of its orbital ellipse, the distance between Mars and
the Sun varies from 206.6 million to 249.2 million km. Mars completes a single orbit in roughly the
time in which the Earth completes two. At its closest approach, Mars is less than 56 million km from
the Earth, but it recedes to almost 400 million km. Most Earth-based observations of Mars are best
made when the planet is in the opposite direction in the sky to the Sun, allowing all-night viewing
when Mars is closest to the Earth.
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