Beginner Level Advanced Level
INTERMEDIATE LEVEL
Content
when needed, when necessary ☊ 
khi cần thiết ☊
→ → →
like: khi cần thiết → →
Children should be disciplined when the need arises (= when it is necessary). ☊ arise ☊
No expense was spared (= they spent as much money as was needed) to make the party a success. ☊ expense ☊
Only use your car when absolutely necessary. ☊ necessary ☊
Changes can easily be made where necessary. ☊ necessary ☊