**Core Concept**
The latent period of muscle twitch refers to the time between the onset of electrical stimulation and the initiation of muscle contraction. The contraction period, on the other hand, is the time during which the muscle contracts. Tetanization occurs when the stimulation frequency exceeds the contraction period, resulting in sustained muscle contraction.

**Why the Correct Answer is Right**
To determine the tetanizing frequency, we need to consider the minimum frequency required to prevent muscle relaxation between successive stimuli. Since the contraction period is 40ms, the minimum frequency should be at least 1/40 Hz to prevent relaxation. However, this is not the correct answer, as tetanization occurs when the frequency is higher than the contraction period. The correct answer is the frequency that is at least twice the contraction period, ensuring that the muscle is always contracting and does not have time to relax.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is below the contraction period, allowing for muscle relaxation.
**Option B:** This option is incorrect because it is equal to the contraction period, which is not sufficient for tetanization.
**Option C:** This option is incorrect because it is less than twice the contraction period, allowing for muscle relaxation.

**Clinical Pearl / High-Yield Fact**
A classic exam trap is to confuse the latent period with the contraction period. Remember that tetanization occurs when the stimulation frequency exceeds the contraction period, which is the time during which the muscle contracts.

**Correct Answer:** D. 2/40 Hz = 50 Hz