Explanation: Equipment for radiotelephony use in survival craft under GMDSS must be designed for critical emergency communication. Here's why option C is correct: * **Operation on Ch-16:** VHF Channel 16 (156.8 MHz) is the international distress, safety, and calling frequency for radiotelephony. This is absolutely essential for a survival craft to communicate with rescuers or other vessels. * **Watertight:** Survival craft operate in a marine environment, often exposed to water and harsh conditions. Being watertight ensures the equipment remains functional during an emergency. * **Permanently-affixed antenna:** In a high-stress emergency, fiddling with a detachable antenna could lead to loss or improper connection. A permanently-affixed antenna ensures the radio is ready for immediate use and reduces the risk of loss or damage. Let's look at why the others are incorrect: * **A) Permanently-affixed antenna, watertight, power 1W or 25W:** While power output options are relevant, specifying both 1W *or* 25W as a requirement can be misleading. Many survival craft handhelds are low power (e.g., 1W or 5W). More importantly, it omits the crucial requirement of operating on Channel 16. * **B) Watertight, power a minimum of 1W, operation on CH-16, Ch-13 & Ch-70:** Ch-16 is vital for radiotelephony. However, Ch-13 (bridge-to-bridge) is not a primary requirement for *survival craft* voice communication, and Ch-70 is specifically for Digital Selective Calling (DSC), not radiotelephony (voice). The question asks about *radiotelephony use*. * **D) Operation on Ch-16, Ch-13 & Ch-70, power 1W, permanently-affixed antenna:** Similar to B, the inclusion of Ch-13 and Ch-70 (DSC) as mandatory for *radiotelephony use* in a survival craft makes this option less precise than C, which focuses on the absolute essentials for voice distress communication. Option C identifies the fundamental and universally mandatory characteristics for survival craft radiotelephony equipment according to GMDSS regulations.