I still remember my first teacher we haven't seen each other for a long time.
A:if
B:until
C:though
D:because
某品牌滚筒洗衣机,筒门处有开关S1,筒门关闭时S1闭合,筒门打开时S1断开.筒门开关S1和控制开关S2必须同时闭合时,洗衣机才能工作.下列符合要求的电路模型是( )
羟基扁桃酸可由苯酚和乙醛酸通过一步反应制得
下列有关说法正确的是( )