**Core Concept**
The power of a lens in ophthalmology is a measure of its ability to converge or diverge light rays, and it is defined as the reciprocal of its focal length measured in meters. The unit of power is the diopter (D), which is equivalent to the reciprocal of the focal length in meters.

**Why the Correct Answer is Right**
The power of a lens can be calculated using the formula: Power (D) = 1 / Focal Length (m). In this case, the focal length is given as 0.75 m. Substituting this value into the formula, we get Power (D) = 1 / 0.75 = 1.33 D, which is closest to option A. This calculation is essential in ophthalmology for determining the power of corrective lenses, such as glasses or contact lenses, needed to correct refractive errors.

**Why Each Wrong Option is Incorrect**
**Option B:** 2.3 D is incorrect because it is higher than the calculated value of 1.33 D. A higher power lens would have a shorter focal length, which is not the case here.
**Option C:** 3.3 is incorrect because it is not in the correct unit (diopters) and is also higher than the calculated value. This option is likely a distractor to test the student's understanding of the units involved.
**Option D:** 4.3 D is incorrect because it is significantly higher than the calculated value of 1.33 D and is not a plausible value for the power of a lens with a focal length of 0.75 m.

**Clinical Pearl / High-Yield Fact**
In ophthalmology, the power of a lens is crucial in determining the prescription for corrective lenses. A common mnemonic to remember the power of a lens is "1/f = P", where "1/f" represents the reciprocal of the focal length and "P" represents the power of the lens.

**✓ Correct Answer: A. 1.3 D**