题目

Shawneen Mountain is a perfect place for skiing. Lifts（电梯）can help tourists get to the top of the mountain in 3 minutes. The following is the price table of the lift tickets.LIFT TICKETSTouristsWeekday(open to close)Weekend(open to close)Night(3 p.m. to 10 p.m.Adult* (Ages 19 to 60)$48$55$34Young Man * (Ages 18＆. under)$37$41$34Child (46cm tall &. under)FREEFREEFREECollege Student[College ID (证件 ) needed]$38$49$34Soldier (Active Duty ID needed)$38$49$34Elders* ( Ages 60 to 69)$38$49$34Super Elders* (Ages 70+)FREEFREEFREE* proof (证明) of age neededLift HoursMonday --- Frida若燃气热水器安装在室内，如果室内通风不良，使用时容易产生一种有毒气体．请回答：（1）该有毒气体是什么？（2）为防止中毒，使用燃气热水器洗澡时，应注意什么？