[多选题]超声波检测条件的主要考虑因素是( )。
A.工作频率
B.探头和仪器参数
C.耦合条件与状态
D.探测面

Theme-park-bound bargain seekers would be wise to spend some time surfing online before they get in line at the parks this summer.
A growing number of these attractions now allow customers to print e-tickets at home with large discounts off the gate price, in part to spur attendance that has declined in recent years.
After boom times in the late 1990s, theme park attendance began to decrease, with an overall decline of about 4% over the past few years at North American’s 50 most-visited establishments, says James Zoltak, editor of Amusement Business. "The bloom was off the rose as we turned the corner into 2000, so there’s more discounting now," he says.
Discounting isn’t new to an industry that has long partnered with other commercial enterprises, such as soft drink companies, to offer deals. But e-ticketing adds a new opportunity that not only brings savings but convenience as well, since it allows visitors to avoid th
A. e-tickets
B. bargains
C. theme Parks
D. discounts