根据下面资料，回答21-25题
The UK's largest airports are set to spend millions of pounds on anti-drone equipment as they seek to protect themselves from attacks such as the one that grounded about 1,000 flights into and out of Gatwick airport during the Christmas period.
It emerged yesterday that the country's two busiest hubs, Heathrow and Gatwick, had already bought in their own military-grade anti-drone apparatus. The owners of both airports have invested millions in the equipment after about 140,000 passengers were affected by unprecedented disruption to Gatwick. The military had to be called in amid a series of reported drone sightings over the course of three days and it is believed that the Israeli-developed Drone Dome system, which can detect and jam communications between a drone and its operator, was deployed.
While Gatwick would not say what equipment had been installed, a spokeswoman said the airport's owners had bought a system that provided a similar level of protection and that had been installed about a week ago. A Heathrow spokeswoman also confirmed that reports of investment in military-grade anti-drone equipment there were accurate.
On Wednesday, the Ministry of Defence confirmed it had withdrawn its resources from Gatwick, though a spokesman said the armed forces "stand ever ready to assist should a request for support be received". It is understood that the transport secretary, Chris Grayling, chaired a top-level meeting yesterday in which defence and police chiefs, together with Home Office officials, discussed how to handle the threat of drones in the future. The aviation minister, Liz Sugg, is also due to meet the heads of the UK's major airports next week to discuss the states of their own defences, and what they plan to put in place in future.
The airports are expected to announce significant investments in further anti-drone systems, though not all will necessarily be in the form and scale of those deployed at the two London airports. A Gatwick spokeswoman said the airport had "invested several million pounds in new equipment which provides a similar level of reassurance as offered by the armed forces". A Heathrow spokeswoman said："The safety of our passengers and colleagues remains our top priority. Working closely with relevant authorities including the Met police, we are constantly looking at the best technologies that help remove the threat of drones."
Last week officers received 115 reports of drone sightings in the area, including 93 that had been confirmed as coming from credible people including a airport staff. Some reports of drones in the area may have involved the police's own craft. It was absolutely certain that a drone had been flying near the airport's runways during the three-day disruption. Police are still searching for those responsible.
It can be inferred from Paragraph 3 that_________

A there are numerous passengers stranding at Heathrow and Gatwick

B anti-drone apparatus may have already been installed at Gatwick

C the anti-drone equipment is to connect a drone and its operator

D the military was called in after the two airports were influenced