Which of the following is/are the physical test(s) employed for the manufacture of paper? I. Mechanical and strength properties II. Surface properties III. Optical properties IV. Permeability to fluids. Select the correct answer using the code given below.

Paper manufacture employs a range of physical tests for quality control. Mechanical/strength tests (tensile, burst, tear strength) ensure the paper can withstand handling — I is used. Surface properties (smoothness, roughness) affect printability — II is used. Optical properties (brightness, opacity, gloss) determine appearance — III is used. Permeability to fluids (porosity, absorptivity) matters for printing inks and packaging — IV is used. All four are standard physical tests employed in the paper industry.