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【单选题】
单片机的P34、P35、 P36 、P37 口分别接LED1、LED2、LED3、LED4,输出低电平点亮LED灯, P20口接按键K1,按键按下时单片机输入低电平,程序如下: #include sbit key = P2^0; unsigned char a ; unsigned char count = 16; void delay(int i) { while(i) i--; } void main() { while(1) { if( key==0 ) { delay(10);// 通过延时来抗干扰 if( key==0) { count--; while(!key); if( count<0) count = 15; a = count; a = ~a; a = a<<4; P3 = a; } } } }A.
减1计数器，按键按一次减一，减至0后重新从15开始减1计数；
B.
减1计数器，定时时间减1，减至0后重新从15开始减1计数；
C.
a = a<<4; 执行结果a左移4位，低4位补0；
D.
a = a<<4; 执行结果a左移4位，低4位补1 。
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举一反三
【简答题】下面程序的功能是:当输入 23 35 时 ,输出变量C的值,请完善程序。 #include int main() { int a,b,c; 1 ; c=a+b; 2 ; return 0; }
【单选题】The American tourist hurried to the museum, only ________ that the train had pulled out of the station．
A.
telling
B.
to tell
C.
to be told
D.
having been told
【单选题】王粲《登楼赋》中,表达作者积极用世之志的句子是 ( )
A.
凭轩槛以遥望兮，向北风而开襟
B.
钟仪幽而楚奏兮，庄舄显而越吟
C.
昔尼父之在陈兮，有归欤之叹音
D.
惧匏瓜之徒悬兮，畏井渫之莫食
【单选题】He ________ the door and ripped the top part of some sort of hinge.
A.
pulled on
B.
pulled up
C.
pulled out
D.
pulled down
【单选题】Not until the train pulled into the station that his suitcase was gone.
A.
had he found
B.
did he find
C.
he had found
D.
he found
【单选题】He ______ between life and death for a few days but then he pulled through.
A.
hovered
B.
lurched
C.
wavered
D.
fluctuated
【单选题】He _____ after the doctor had almost given him up. [ ]
A.
pulled down
B.
pulled up
C.
pulled through
D.
pulled off
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