At present, scientists expect the universe to gradually stop its expansion and then begin to shrink in size gradually stop its expansion and then remain at a constant size gradually stop its expansion, pause, and then resume expanding continue to expand and heat up forever continue to expand and cool forever

The answer is the fourth option: At present, scientists expect the universe to continue to expand and cool forever.

The correct answer is the last statement, that is, continue to cool and expand.

Explanation:

The notion of expanding universe was for the first time discovered by Einstein's theory. The outcomes attained via his theory of relativity has the redshifting of light when they come from distant objects moving all through the expanding universe. Later in 1929, it was further stated by Hubble that universe is expanding when he deduced the curve between the redshift against the relative distance.  

From this it was further proved that because of the expansion of universe there can be an influence of redshift in the spectrum of light as the wavelength would have turned lengthier in comparison to the earlier that would result in the reduction in temperature related to the spectrum and hence the universe keeps on cooling spontaneously as it expands simultaneously.  

the  frequency of a wave represents  the number of wavelengths that pass a specific point per second. the unit for  frequency  is hertz (hz).

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the answer to your question is:

c. complementary base-pairing