(a) specificity is the ability of an enzyme to choose exact substrate from a group of similar chemical molecules. The specificity is actually a molecular recognition mechanism and it operates through the structural and conformational complementarity between enzyme and substrate.
The ability of enzyme to bind with specific substrate or catalyze a specific set of chemical reactions,is called "enzyme specificity".Some enzyme have an intrinsic property of binding with only one substrate and catalysing a single reaction.This property is called "Absolute specificity".E.g Urease enzyme acts on Urea.
(b) fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes called fatty acid synthases. This process takes place in the cytoplasm of the cell. Most of the acetyl-CoA which is converted into fatty acid is derived from carbohydrates via the glycolytic pathway.
(c) Simply, recombinationis the production of new DNA molecules from two parental DNA molecules or different segments of the same DNA molecule. The genetic recombination causes re-arrangement of genes producing altogether new genotypes and phenotypes. These cause variations which lead to evolution.Molecular recombination means Exchange, replacement, or insertion of sequences especially between, of, or into DNA molecules molecular recombination is the consequence of crossing over during meiosis, though involves additional mechanisms including in non-eukaryotes.