水平杆上套有两个质量均为m的环，两细线等长上端系着环，下端系着质量为M的物体，环及物体组成的系统静止，现在增大两环间距而系统仍静止，则杆对环的支持力N和细线对环的拉力F的变化情况是（　　）

A．都不变

B．都增大

C．N增大，F不变

D．N不变，F增大

Programmers test a program by running it to ensure that the (74) are correct and that the program produces the desired outcome. If errors do occur, the programmer must make the appropriate change and recheck the program until it produces the correct results. This (75) is called testing and debugging.

A．procedure

B．program

C．programmer

D．process