Q:I'm taking a test and have to guess the right answer to the question after the article. Article: The secret of carrier pigeons' unbelievable ability to find their way home has been discovered by scientists: _ follow the roads just like we do. Scientists now believe the phrase "as the crow flies" no longer means the shortest most direct route between two points. They say it is likely that crows and other day birds also choose AA-suggested routes, even though it makes their journeys longer. Scientists at Oxford University spent 10 years studying homing pigeons using global positioning satellite (GPS) and got a surprising result. The birds often don't use the sun to decide their directions. Instead they fly along motorways, turn at crossing and even go around roundabouts , adding miles to their journeys. "It really has knocked our research team sideways to find that after a decade-long international study, pigeons appear to ignore their inbuilt directional instincts and follow the road system," said Prof Tim Guilford, reader in animal behavior at Oxford University's Department of Zoology. Guilford said pigeons use their own navigational system when doing long distance trips or when a bird does a journey for the first time. "But once homing pigeons have flown a journey more than once, they can fly home on a habitual route, much as we do when we are driving or walking home from work," said Guilford. "In short, it looks like it is mentally easier for a bird to fly down a road. They are just making their journey as simple as possible." Question: Scientists used to think that homing pigeons often find their directions _ . Options: A: by global positioning satellite B: by the sun C: by the road system D: by following other birds
A:
B