When I went back to my hometown three years ago I found that a lot of changes blank which verb phrase correctly completes the sentence.

Introduction / Context:
This question examines tense sequence and correct verb phrase formation in English. The sentence describes two actions in the past: the speaker went back to the hometown three years ago and discovered that many changes had already occurred by that time. The goal is to select the verb phrase that correctly expresses this earlier completed action relative to another past event.

Given Data / Assumptions:

• Main clause: “When I went back to my hometown three years ago, I found that a lot of changes blank.”
• Four possible completions: were taken place, are taken place, had taken place, have taken place.
• The reference point “three years ago” clearly indicates past time.
• The changes happened before the moment of discovery.

Concept / Approach:
We are dealing with two events in the past. To show that one past event was completed before another past event, English uses the past perfect tense. In this sentence, returning to the hometown and finding the changes is one event in simple past. The changes themselves happened before that visit, so they must be expressed in past perfect as “had taken place.” We also must avoid incorrect passive constructions such as “were taken place” and wrong present tense forms like “are taken place” or “have taken place.”

Step-by-Step Solution:
Step 1: Identify tenses already used. “Went back” and “found” are simple past forms, fixing the main action in the past. Step 2: Decide the relative order of actions. The changes must have occurred before the speaker returned, because they were already present to be found. Step 3: Apply the rule that an earlier past action is expressed using past perfect, constructed as had plus past participle. Step 4: Recognise that “taken place” is the past participle form of the phrasal expression “take place,” so “had taken place” is the correct past perfect. Step 5: Reject forms that misuse passive voice or present time for a clearly past situation.

Verification / Alternative check:
If we restate the sentence more fully, it becomes “When I went back to my hometown three years ago, I found that a lot of changes had already taken place.” In this expanded version, the use of “had already taken place” clearly signals that the changes happened earlier than the visit. This structure is standard in narratives describing a sequence of past events. By contrast, “were taken place” is ungrammatical, as “take place” does not normally form a passive. “Are taken place” and “have taken place” wrongly suggest present time or a link to the present moment, which conflicts with “three years ago.”

Why Other Options Are Wrong:

• Were taken place: Incorrect passive construction. We say “took place” or “had taken place,” not “were taken place.”
• Are taken place: Uses present tense and passive, both inappropriate for a time reference in the past.
• Have taken place: Present perfect tense connects past to present, but the sentence frames everything around a specific past time point.

Common Pitfalls:
Many learners are tempted by present perfect because they associate “change” with a result that is still visible. However, once the time is clearly fixed in the past, especially with expressions such as “three years ago,” English normally uses simple past or past perfect, not present perfect. It is important to separate narrative sequence from present relevance in such contexts.

Final Answer:
The correct and natural completion is had taken place, giving the full sentence “I found that a lot of changes had taken place.”