How may mRNA be modified before it leaves the nucleus?

The pre-mRNA molecules undergo three main modifications. These modifications are 5' capping 3' polyadenylation and RNA splicing which occur in the nucleus before RNA is translated.

Explanation:

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

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what is a measurement of the earth’s history divided into time periods?

> fossil record <

sedimentary rock

> geologic time scale <

radioactive elements