What is the single most important reason
that astronomers have learned more about
our planetary system in the last 30 years than
all of history before then?
1. the Hubble Space Telescope
2. Radio telescope arrays allow astronomers
to make out details on the planets that they
have never been able to see before.
3. Astronomers today are a lot smarter than
astronomers were earlier.
4. We have been able to send spacecraft to
visit many planets and satellites.
5. The planets (moving in their slow orbits
around the Sun) hyppen to be closer to the
Earth in the last 30 years than at any previous
time in human history.

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

if it's not useful, feel free to report for mistake in answer.

shield volcanos are angry and get mad over the smallest things so much that there heads erupt   pahoehoe and a'a lava. a composite volcano is the poller opposite of a shield volcano. its   peaceful thing and knows how to control its emotions.