請依下文回答第 46 題至第 50 題：
 A wet spring in Las Vegas has spawned hordes of grasshoppers so large that they are showing up on the weather radar.In viewing the radar, CNN meteorologist Allison Chinchar said it looked like there were two storms over the Vegas area:one in the north of the city (that was actual rain) and another right over Las Vegas. But the second one wasn’t moving asrain normally would, she said. “It looked as though it should be torrentially downpouring in Las Vegas,” said Chinchar.By changing the settings on the radar, meteorologists could see that the other “storm” was actually the massive hordesof grasshoppers that have settled over the city in recent days, Chinchar said. Las Vegas, like all of Nevada, has had almosttwice as much rain in 2019 than normal, Chinchar said. “It appears through history that when we have a wet winter orspring, these things build up often down below Laughlin and even into Arizona,” Jeff Knight, state entomologist, said.“We’ll have grasshopper migrations about this time of the year, and they’ll move northward.” Knight said the swarmsaren’t terribly unusual given the amount of rain the state has had this year. “We have records clear from the ’60s of ithappening, and I have seen it ... at least four or five times in my 30-plus years,” he said. “There are some special weatherconditions that trigger the migration.”
【題組】46 Which of the following is the topic of this passage?
(A)Las Vegas’ grasshopper invasion is so big that you can see it on weather radar.
(B)Grasshoppers lead to more rain in Las Vegas.
(C)Las Vegas’ grasshoppers have started their migration earlier than usual.
(D)Las Vegas’ deserts are soon disappearing due to vast amounts of rain.