Mock, V. E. (1982). Subtraction drill for levels 1-3. David S. Lake Publishers.
芝加哥风格引文Mock, Valerie E. Subtraction Drill for Levels 1-3. Belmont, Calif: David S. Lake Publishers, 1982.
MLA引文Mock, Valerie E. Subtraction Drill for Levels 1-3. David S. Lake Publishers, 1982.
警告：这些引文格式不一定是100％准确.