Read the text carefully, then answer the question located beneath:

time to "bee" wary, by gordon winters

africanized honey bees were created in brazil in 1957. scientists mixed local bees with african ones to create a bee that would make more honey. they ended up with something much different. the new bees evolved in unexpected ways. they multiplied and migrated north. these africanized honeybees are now known as killer bees for several scary but legitimate reasons.

killer bees are far more aggressive than their relatives. they have been known to attack in great numbers, even when there has been no direct threat on their hives. they have swarmed because of loud noises, dark clothing, bright jewelry, and even strong perfume. they will chase a person for more than a quarter of a mile and remain angered for up to 24 hours.

killer bees are also dangerous because of their sting. while most bees take up to 30 seconds to attack, killer bees sting in just 3 seconds. their venom is no stronger than a regular bee's, but when one killer bee stings, others follow. with up to 80,000 members in a colony, victims are quickly overwhelmed. so many stings in such a short time can cause allergic reactions. victims enter a state of shock, lose blood pressure, and in many cases, die.

a final reason why "killer" has been added to their name is the unfortunate number of deaths they have caused. experts estimate that the africanized honeybee moves at a rate of about 200 miles each year. as the bees claim new territory, they claim new victims as well. more than 1000 people have been stung to death in south and central america. there have been rising numbers of attacks in mexico and a handful in the united states. once a swarm sets sights on a victim, it is very difficult for the victim to escape. once attacked, it is very difficult to survive.

, there has been no killer bee invasion as some once predicted. although there is no need for panic, the threat of the killer bee is real and should be taken seriously. it is good practice to call a professional to remove beehives in your area. if you are stung multiple times by any insect, you should always seek medical attention. you may not be expert enough to tell the difference between a killer bee and a less dangerous one, so be smart. it is better to be safe than sorry.

which sentence from the introduction paragraph serves as the author's thesis?

africanized honey bees were created in brazil in 1957.
scientists mixed local bees with african ones to create a bee that would make more honey.
a group of the bees escaped and joined local bees to create new colonies.
africanized honeybees are now known as killer bees for several scary but legitimate reasons.