In the same passage about photography and memory, select the correct verb form to complete the phrase "the photo album is the most potent time machine ever ____________, one that transports you to a curated past".

Introduction / Context:
This cloze item focuses on the correct past participle form in a passive construction. The sentence reads The photo album is the most potent time machine ever blank, one that transports you to a curated past. The idea is that among all devices humans have created, the photo album is the most powerful time machine. In English, the phrase ever built is a standard way to describe something as the greatest of all things that have been constructed.

Given Data / Assumptions:
- The structure around the blank is is the most potent time machine ever blank. - The options are build, built, building, and builds. - We recognise that ever often accompanies a past participle in sentences like the best film ever made. - The intended meaning is that at any time in history, no time machine created has been more potent.

Concept / Approach:
In English, we say the best book ever written, the largest ship ever built, and the most beautiful song ever sung. In each case, the past participle form of the verb appears after ever to form a reduced relative clause. Built is the past participle of build. The other forms are either base form build, present participle building, or present tense builds, none of which correctly fit this pattern. Therefore, we must choose built to complete the passive sense implied by ever built.

Step-by-Step Solution:
Step 1: Recall that build has the forms build, built, built for base, past, and past participle. Step 2: Compare with similar examples: the greatest monument ever built, the strongest bridge ever made. Step 3: Test option A: The time machine ever build. This is ungrammatical because build is not in the correct form. Step 4: Test option B: The time machine ever built. This matches the known pattern and sounds natural. Step 5: Test option C: The time machine ever building. This does not create a meaningful passive construction. Step 6: Test option D: The time machine ever builds. This changes the meaning completely and does not fit the structure after most potent.

Verification / Alternative check:
We can expand the reduced clause for clarity: the most potent time machine that has ever been built. Here, built clearly functions as the past participle in a passive perfect construction. When clauses are reduced, the auxiliary has been is often dropped, leaving ever built on its own. This is exactly what is happening in the passage. Substituting any other form breaks the underlying grammar. Thus, the only correct choice is built.

Why Other Options Are Wrong:
Option A, build, is wrong because the base form cannot serve as a passive participle in this context. Option C, building, is wrong because it is the present participle and would suggest an ongoing action, which is not the intended meaning. Option D, builds, is wrong because it is a present tense verb and would need a subject, not fit after ever in this structure.

Common Pitfalls:
Learners sometimes forget that certain fixed expressions combine ever with a past participle. When you see ever followed by a verb in such comparative structures, you should look for the past participle form and think of the full relative clause that has been omitted. Recognising patterns like ever built, ever seen, and ever written is very helpful in cloze passages, as they repeat frequently across reading materials and exam questions.

Final Answer:
The correct answer is built.