A far-sighted person has difficulty seeing objects up close, and their near point is farther away than the average person. To correct their vision, a convex lens is used. The power of a lens is measured in diopters (D), with positive values for convex lenses.

Option 1: -0.8 D - This option represents a concave lens, which cannot correct far-sightedness. Therefore, this option is incorrect.

Option 2: -3.0 D - This option also represents a concave lens, which is not suitable for correcting far-sightedness. Hence, this option is incorrect.

Option 3: +0.8 D - This option represents a convex lens, which can be used to correct far-sightedness. However, the power of +0.8 D may not be sufficient to correct a person with a near point at 100 cm. Hence, this option is incorrect.

Option 4: +3.0 D - This option represents a convex lens with a power of +3.0 D. This strong convex lens would be suitable for a far-sighted person with a near point at 100 cm. Therefore, this option is correct.

In conclusion, the correct answer is Option 4, +3