试题题干
Fill in each of the following blanks with a word or an expression.
The constituents which may be present or absent on the right side of the arrow in a phrase structure rule are called 
constituents.
参考答案
试题解析
在短语结构规则中，箭头右侧可能存在或不存在的成分被称为可选成分。
Fill in each of the following blanks with a word or an expression.
The constituents which may be present or absent on the right side of the arrow in a phrase structure rule are called constituents.
在短语结构规则中，箭头右侧可能存在或不存在的成分被称为可选成分。