For a mutation to affect evolution it has to be passed on to all the offspring if that is what you mean.
A jet stream forms high in the upper troposphere between two air masses<span> of very different temperature. The greater the temperature difference between the air masses, the faster the wind blows in the jet stream.
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So "Differences in temperature between two air masses" is the answer
April is the <u>fourth month</u> of the year in the Gregorian calendar, the fifth in the early Ju.lian, the first of four months to have a length of 30 days, and the second of five months to have a length of less than 31 days.
