The activities of enzymes are determined by their three dimensional structure. which of the following gives a three dimensional structure to an enzyme? folds of long, linear chains of amino acids folds of long, linear chains of fatty acids folds of long, linear chains of covalent hydrogen bonds

d. struggle for existencee.

Explanation:

Malthus's essay main theme was that- population size  will always undergo an exponential growth; and as this continues this  supersedes available food supply growth. The negative effects of this on the population is struggle for survival for limited food available leading to hunger, famine and death.

The word ' struggle' for survival  in Malthus essay intrigued Darwin's, and this formed the  basis of his theory.

Darwin discerned that some organisms within the population will be able to struggle and survive and therefore   withstand the selective pressure of limited food supply, while those without ability to struggle will die of hunger,and  diseases. He concluded that,  the ability to  struggle for existence by  some members of the population , was due to some inheritable characteristics which they must have inherited from  their previous generation. While those that could not withstand the selective pressure, died of hunger .

Basically, variation(not mentioned by Darwin) was the factor that ensure  struggle for  existence for the survival of the fittest, and nature will select the fittest compare to those without variation. The organisms without ability to struggle will die, and the  new population  with ability to struggle to survive will evolved.- this is the theory of evolution, this is Dawin's theory of natural selection.