You are studying a protein and notice that it contains two regions made of beta-sheets connected by an alpha-helix. This type of recurring structure that can be found in proteins with very different functions is called a:

Motif

Explanation:

Motif (super secondary structures) are similar three dimensional structure conserved in different proteins and perform the similar function. But we cannot predict the function of a protein from the presence of motif because there are several proteins and enzymes that have the same motif but perform different functions.

Structural motif in protein describe the interaction between secondary structures such as helix-turn-helix.

Example; Beta hairpin is an example of motif in which a strong turn of few amino acids connect the two strands

in 1859, charles darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. he defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved".