单项选择题
Directions：Please choose the best answer from the following 4 choices, and fill in the blanks with the corresponding letter. We were early for our appointment, so we _____ at a bookstore. A、race against time B、time has come C、time out D、kill time
单项选择题 人首先必须活着，然后才能做别的事情。
判断题 继电器一般用来直接控制有较大电流的主电路。
问答题 ST编程的一个表达式中包括什么？
