单项选择题词汇题 （Fill in the blanks by choosing from the words below. Change the forms where necessary.) Fear of making mistakes is one of the main (____) to mastering spoken English.
单项选择题对成本差异控制的重点在于（ ）。 A、可控差异 B、不可控差异 C、有利差异 D、不利差异
