题目内容：
根据下面内容，回答题： Toronto : A 300-pound adult Siberian tiger escaped from its four-meter high chain-link pen ( 圈 )at the Toronto Zoo yesterday, on one of the busiest days of the year.
Though no one was hurt, the dangerous animal was separated from the public for a time by nothing more than a four-meter fence. The escape occurred after one of the animal's handlers left the pen gate open. It prompted a swift response from officials. Staff were sent immediately to arrest the runaway tiger.
General Manager Calvin White told reporters that staff were preparing for the worst. "I ordered a tranquilizer (麻醉剂) gun so we would have tranquilized her, but thankfully we didn't have to," Mr.White said. The tiger was successfully led back into its cage after the brief escape.
The incident occurred during the Toronto Zoo's 28th annual Christmas Treats Walk, where admission is free in return for donations of food that does not easily go bad.
Thousands of people attend each Boxing Day to see the animals fed by their handlers.
The tiger escape happened________. A．owing to the lack of food
B．due to its separation from the public
C．because of the handler's neglect of duty
D．as a result of the damaged chain and fence________.
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