Question

decide whether each function is carried out by lipids, proteins, or carbohydrates in the cell membrane.
allow the cell to be recognized by other cells
give the membrane its flexibility
pump large molecules across the membrane

Explanation:

Carbohydrates on the cell - membrane surface form glycoproteins and glycolipids which act as recognition markers for cell - cell recognition. Lipids, especially the phospholipid bilayer, give the membrane its flexibility. Proteins, such as transport proteins, are responsible for pumping large molecules across the membrane.

Answer:

Allow the cell to be recognized by other cells: Carbohydrates
Give the membrane its flexibility: Lipids
Pump large molecules across the membrane: Proteins