The phrase "sine qua non" in Para. 5, Line 1 possibly means ______.

A．give a brief account of California and its problems
B．inform us why California is so attractive and enduring
C．promote and popularize a would-be classical book
D．make a comment on Mr. Start and a review of his masterpiece

A．The distributional imbalance of each of the part.
B．The chaotic arrangement and design of the structure.
C．The improper selection of some materials.
D．The cautious view and attitude of the writer.