题目

       The advantages of using flashcards to build up a vocabulary are well known. You can buy sets of cards, or make your own, and carry them with you wherever you go. There’s no question this is useful and because you can use them in short bursts, it’s not too much for you. It can be fun. I don’t recommend drilling for hours at a time with flashcards.        If you want to use flashcard software, things get even better. There are many packages out there for maintaining and drilling flashcards. I recommend VTrain though there are many others.        One stands使用天平和量筒测量金属块的密度时，将天平放在水平桌面上，发现指针指在分度标盘中央刻度线的左侧，此时应将天平的平衡螺母向（选填“左”或“右”）调节．用调好的天平测金属块的质量时，砝码及游码的位置如图甲所示，则金属块的质量是g；放入金属块前量筒内水的体积为10ml，放入金属块后量筒内水面位置如图乙所示，则金属块的密度为kg/m3 ． 若金属块有磨损后，它的密度（选填“变大”、“变小”或“不变”）．