以羟基氧化铝为基础的乳化钻井液，密度可控制在（）g/cm³的范围内。

A、0.88~0.97

B、0.5~0.77

C、1.00~1.20

D、1.5~2.0

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