单项选择题 The scavenging box is built of a number of sections provided with vertical flanges enabling them （） together to form two blocks.

单项选择题 The scavenging air ports are located at （） that they are just exposed by the upper edge of the piston when the piston is in the bottom dead center position.

单项选择题 The rising of the exhaust temperature in manifold pipe may NOT result from （）.