A．To account for the comet's composition of ice and dust.
B．To show the effect of Jupiter's gravity on the comet's orbit.
C．To explain why the comet is not visible from Earth very often.
D．To argue that the comet's orbit should not be considered periodic.
A．It moves slower.
B．It starts to heat up.
C．It loses some material.
D．It absorbs gases from the Sun.
A．It has always had the same orbit it has now.
B．It used to be much smaller than it is now.
C．It did not always have the same orbit it has now.
D．It is much younger than the rest of the solar system.
A．It is not possible to study their thinking habits.
B．They solve problems in a totally different way.
C．Their muscular movements are not stimulated by ideas.
D．The muscles in their hands move when they solve problems.