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Athin layer, whichsurrounds the membrane of the cell and provides support to the membrane is known as apellicle. It functions as a protecting covering or flexible coat, which protects the cell from getting pierced.

Protists can be surrounded by acell membrane, a cell wall, silica-based shells, or a pellicle. The shells are formed of calcium carbonate and silica dioxide. Carbohydrates are the constituent part of the cell wall. Therefore, the pellicle is not surrounded by calcium carbonate, silica dioxide, or carbohydrates.

Thus, optionsa, b and c are incorrect.

Some of the protists are encircled by a thin outer layer known as a pellicle, which offers protection to the cell. It is a flexible coat of armor, which envelopes the membrane of the cell. The pellicle is surrounded by interlocking protein strips.

Hence, the correct answer isoption d.