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-foot 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 run-away 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 ____.（ ）
文章第二段第二行The escape occurred...left the door open.可以看出事故发生的原因是工作人员没有尽到责任。
