Final answer:
Commanders conduct drug testing on 100% of Trainees after HBL to ensure compliance with the military's strict no-drug policy.
Step-by-step explanation:
The question relates to the percentage of Trainees who are subject to drug testing upon their return from Holiday Block Leave (HBL). The correct answer is D) 100. The rationale for this is due to the military's stringent policy on drug use. Commanders are expected to maintain a drug-free environment, and as such, they mandate drug testing upon return from HBL to ensure that all service members comply with military drug use policies.