题目

  When you’re on the go, your best friend and resource can be your phone. In the age of smart phones, apps are like guiding stars: They can point you in the right direction for a hotel, list expenses, send postcards, and much more. When used together, these apps can be the basic travel tool, placing a wealth of information at your fingertips no matter where you are on the planet. U.S. News Travel has picked the essential travel apps, known for their utility and reliability. Best of all, they cost absolutely nothing. Trip It Your Personal Travel Agent      Be your own travel agen和青蛙相比，鸟的成活率高，主要原因包括（ ）①体内受精 ②卵生 ③体外受精 ④卵外卵壳做保护 ⑤亲鸟有孵卵育雏行为 ⑥胎生A．①④⑤ B．②③ C．①②④⑤ D．①④⑤⑥