2008年1月12日我国科考队员登上了南极“冰盖之颠”。他们生理上出现的适应性变化是

①体温下降 ②机体耗氧量降低 ③皮肤血管收缩 ④体温调节中枢兴奋性增强 ⑤甲状腺激素分泌量增加[ ]

A．①③④

B．①④⑤

C．②③⑤

D．③④⑤

Rapid application development (RAD) systems purport to lighten the developer’s (46) by making it easy to program an application with simple intuitive steps.

RAD tools (47) the developer everything needed to construct a fully functional application quickly and easily. They make short work of modifying the developed product to (48) changes after the program is finished. Applications developed with RAD tools are constructed as they are envisioned. As an application’s real usefulness (49) , the developer armed with RAD tools should be able to (50) on new features with little fuss.

（50）是（）

A.beat

B.change

C.debug

D.tack