Explanation: When a pulse RADAR is radiating, it's in its transmit phase, sending out a high-power RF pulse. The TR (Transmit-Receive) box, containing the TR and ATR tubes, is critical for managing this power. The **TR tube** (Transmit-Receive tube) energizes and conducts during transmission. Its primary function is to protect the sensitive receiver from the high power of the outgoing transmit pulse by shunting or reflecting this energy away from the receiver input. Simultaneously, the **ATR tube** (Anti-Transmit-Receive tube) also energizes. During transmission, the ATR tube acts as a resonant switch, effectively creating an open circuit a quarter-wavelength from the antenna connection point. This ensures that the high-power transmit pulse is directed efficiently to the antenna, preventing it from being lost in the receiver path. Therefore, both the TR and ATR tubes are energized during the transmit phase to route the RF power to the antenna and protect the receiver, making option C correct. Options A, B, and D are incorrect because both tubes have distinct but complementary roles during transmission.