In this English grammar question, you must select the alternative that best improves the bracketed part of the sentence; if no improvement is required, choose the option labelled no improvement: Yes, amazing things (has happen) with the launch of the internet.

Introduction / Context:
This English grammar question asks you to improve the verb phrase in the sentence Yes, amazing things (has happen) with the launch of the internet. The focus is on correct tense and subject verb agreement in present perfect structures. Such questions are very common in competitive exams that test accurate written English.

Given Data / Assumptions:
The subject in the main clause is the plural noun phrase amazing things. The bracketed verb phrase has happen is clearly ungrammatical. You need a grammatically correct alternative that fits both the plural subject and the time reference implied by the launch of the internet, which refers to a completed action with results that continue into the present.

Concept / Approach:
When we describe completed actions that have present relevance, we normally use the present perfect tense. The structure of the present perfect for plural subjects is have plus past participle. Therefore, with the subject amazing things we must use have plus the past participle of happen, which is happened. Any form that breaks this pattern will be incorrect for standard formal English in exam contexts.

Step-by-Step Solution:
Step 1: Identify the subject of the clause, which is the plural noun phrase amazing things.Step 2: Recognise that the sentence describes completed events connected to the present, so it requires the present perfect tense.Step 3: Recall the rule that present perfect for a plural subject uses have plus past participle.Step 4: Form the correct verb phrase have happened and insert it into the sentence.Step 5: Read the full sentence Yes, amazing things have happened with the launch of the internet and confirm that it sounds natural and grammatically correct.

Verification / Alternative check:
You can verify the answer by replacing the plural subject with a singular one. With a singular subject such as something amazing, the form would be has happened. That confirms that has goes with a singular subject while have goes with a plural subject. Since amazing things is plural, have happened is the only correct present perfect choice among the given options.

Why Other Options Are Wrong:
is happening uses the present continuous, which suggests an action in progress, not a series of completed changes over time. had happen is wrong because had must be followed by the past participle happened, not the base form happen. has happened is grammatically correct in isolation but does not agree with the plural subject amazing things, so it sounds wrong in standard written English. The option no improvement is incorrect because the original phrase has happen is clearly ungrammatical.

Common Pitfalls:
Candidates often confuse has and have with plural and singular subjects or forget to use the past participle after any auxiliary form of have. Another common error is using the continuous tense is happening when the context clearly refers to an overall result that has already taken place. Always match the auxiliary to the subject and ensure that perfect tenses use the past participle, not the base form of the verb.

Final Answer:
The correct improvement of the bracketed verb phrase is have happened, giving the final sentence Yes, amazing things have happened with the launch of the internet.