例句與造句

1. These rules of engagement were based on the situation in 1968, when North Vietnam's surface-to-air missiles were controlled by fire control radars with a high-pulse recurring frequency, which keyed an alarm in the USAF aircraft . By late 1971, shortly after Lavelle had taken command of 7th Air Force, the North Vietnamese had begun networking their long-range search radars with the missile sites.
2. It's difficult to find recurring frequency in a sentence. 用recurring frequency造句挺難的