（辨析主题句）Read the following paragraph and choose the best topic sentence from the four options that follow. Write the corresponding letter of your choice in the blank provided.
The automobile is a very complicated piece of machinery. It contains thousands of parts connected and fitted so that they all work together. In many instances, the failure of one part will cause the failure of one or more other parts. Extensive repairs are then required. Most part failures cannot be blamed on defects in the parts. Lack of proper adjustment, insufficient lubrication (润滑), and corrosion(锈蚀) cause many failures. Proper maintenance will eliminate many of these causes, and thus minimize part failures. Meanwhile, the most efficient type of maintenance is preventive maintenance. Preventive maintenance emphasizes the simple jobs. Checking and adjusting the level of oil in an engine is a simple job. Yet if the oil level drops too low, extensive engine damage will result. Checking and adjusting the air pressure in tires is another simple job. Yet under inflation is the most common cause of excessive tire wear.
Your choice:
A
Air pressure in tires must be adjusted to reduce excessive tire wear.
B
The automobile is a complicated machine and requires regular checking.
C
Lack of proper maintenance may lead to many part failures in an automobile.
D
Proper automobile maintenance, especially preventive maintenance, is important.
