An be inferred from the passage that: a. in an extinction event, there is a dramatic decrease in microbial life on earth. b. over 90% of easily observed, biologically complex species become extinct during a biotic crisis. c. the background extinction rate of animal and plant species is well below 50%. d. marine fossils are easier to find and thus more useful to those studying mass extinction events.

C. the background extinction rate of animal and plant species is well below 50%.

Explanation:The Reading Comprehension themed ”An extinction event (also known as a mass extinction or biotic crisis)” was the reference source for the answer.

Option C is correct, it requires that one joins two pieces of information. The start of the 3rd paragraph we see that “the five major mass extinctions have significantly exceeded the background extinction rate” and we later saw that ”the rate of those mass extinctions is over 50%.” This brings one to submit that the background rate of extinction is altogether, below 50%.

a time line cause it goes from 685 to 978

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.