http://www.liu.edu/cwis/cwp/library/workshop/citation.htm

“When you borrow from a source several times in succession, you may be able to make your citations more concise by using one of the following techniques. However, always give your citations in full if these techniques would create ambiguity about your sources.

You may be able to combine citations in a single parenthesis after a sequence of borrowings:

Romeo and Juliet presents an opposition between two worlds: “the world of the everyday . . . and the world of romance.” Although the two lovers are part of the world of romance, their language of love nevertheless becomes “fully responsive to the tang of actuality” (Zender 138, 141).

Here it is clear that the first page number in the parenthesis”

http://www.mla.org/style_faq