They have studied English for about five years.（保持原句意思不变）They have studied English_____about five years_____.
问题描述：
They have studied English for about five years.（保持原句意思不变）
They have studied English_____about five years_____.
答
since ； ago
答
They have studied English for about five years.（保持原句意思不变）They have studied English【 since 】about five years【 ago 】.
不明白的再问哟,请及时采纳,多谢!