Answer: A. Removal of a water molecule between each two units
Explanation: Carbohydrates are the those kinds of polymers which are made by the linkage of monomer units of monosaccharides.
Amino acids are the building blocks of the proteins or in other words, we can say that the amino acids are those smallest units from which the polymer like protein is formed.
Thus when 2 monomer units of monosaccharides are joined, condensation reaction will occur with the removal of the small unit like a molecule of water. Same thing happens with the formation of the protein.
Thus option (A) is the correct option.