Combination of smoke and fog is named _____________.
A. Dew
B. Rain
C. Snow
D. Smog

Hint: Smoke is a sol of solid particles like carbon, dust which are dispersed in air. Fog is condensed droplets of water within the air. A mix of smoke which gets stuck within the air with fog may be a common phenomenon within the winter season.

Complete Answer:
A yellowish or blackish fog is named smog. Smoke and fog combine to make smog. It's mainly formed by a mix of pollutants within the atmosphere which consists of fine particles and ground level ozone. Smog occurs mainly due to pollution. Smog also refers to hazy air that creates breathing difficulty. It causes various respiratory problems also as irritation in eyes.
Smog may be a quiet pollution, originally named for the mixture of smoke and fog within the air. Classic smog results from large amounts of coal burning in a neighborhood and is caused by a mix of smoke and sulphur dioxide.
Smoke and fog combine to make smog. It's mainly formed by a mix of pollutants within the atmosphere which consists of fine particles and ground level ozone. Smog also refers to hazy air that creates breathing difficulty. It causes various respiratory problems also as irritation in eyes.

Correct answer is option D.

Note:
Smoke particles are an aerosol or mist of solid particles on the brink of ideal range of sizes for scattering of light. Fog may be a collection of liquid droplets or ice crystals suspended within the dispersion phase as gas near the surface.