Sentence improvement — Perfect tense with ‘‘since + past point in time’’: confirm whether ‘‘I have lived in Delhi since I was four’’ already uses the correct aspect and therefore needs no change.

Given data
Target sentence: ‘‘I have lived in Delhi since I was four.’’

Concept/Approach
With a starting point in the past that continues up to now (‘‘since I was four’’), the present perfect is standard and correct: ‘‘have lived.’’

Option analysis
am living — Present progressive misses the continuity from a past starting point.lived — Simple past suggests the action is finished.had lived — Past perfect needs a later past anchor.No improvement — Best choice; original is already correct.have been living — Acceptable in some contexts but not necessary; the simple present perfect is concise and correct.

Verification/Alternative
Also fine: ‘‘I have been living in Delhi since I was four’’ (continuous nuance). The given version is not erroneous.

Common pitfalls
Switching to simple past with ‘‘since…’’ or using present progressive without the perfect aspect.

Final Answer
No improvement