Red and dry skin. (I'm a Nursing major)
Answer:
The correct answer is single,double and triple covalent bonds .
Explanation:
A carbon atom can form a single bond with another carbon atom example ethane.
A carbon atom can form a double bond with another carbon atom example ethylene
A carbon atom can form a triple bond with another carbon atom example acetylene.
But during the formation of Carbon carbon single bond or double bond or triple bond the valency of carbon atom that is 4 is always maintained.
Answer:
The Earth is essentially a closed system; it obtains lots of energy from the Sun but the exchange of matter with the outside is almost zero. Isolated systems can exchange neither energy nor matter with an outside system.
The Precambrian was originally defined as the era that predated the emergence of life in the Cambrian Period. It is now known, however, that life on Earth began by the early Archean and that fossilized organisms became more and more abundant throughout Precambrian time.
Unlike natural selection, genetic drift does not depend on an allele's beneficial or harmful effects. Instead, drift changes allele frequencies purely by chance, as random subsets of individuals (and the gametes of those individuals) are sampled to produce the next generation.
All the above is correct.
