In this English sentence improvement question, you must select the best version of the sentence "I think so she will come to the party" so that it becomes grammatically correct and sounds natural in standard English.

Introduction / Context:
This question focuses on correcting an everyday English sentence by removing unnecessary words and fixing the normal word order. Examinations often test whether candidates can recognise redundant or misplaced words such as "so" when used wrongly in clauses like "I think so she will come".

Given Data / Assumptions:

• Original sentence: I think so she will come to the party.
• The speaker wants to express a simple opinion about the likelihood of someone coming to a party.
• The task is to pick the option that gives a natural and grammatically correct sentence.
• The tone is neutral, and the tense is simple present combined with simple future.

Concept / Approach:
In English, "I think" is often followed directly by a clause beginning with "that", which can be omitted in informal speech: "I think (that) she will come to the party." The word "so" is used differently. It can stand in for an entire clause, as in "I think so", but when the clause itself is stated ("she will come to the party"), "so" is not used before it. In addition, continuous forms like "I am thinking she will come" are far less natural for a simple opinion about the future.

Step-by-Step Solution:
Identify the core meaning: the speaker believes she will come to the party.Recognise that "I think" introduces a noun clause giving the content of the thought.Remove the unnecessary "so", because the clause "she will come to the party" is explicitly stated.Use the normal pattern: "I think (that) she will come to the party."Confirm that the resulting sentence is clear, grammatically correct, and idiomatic.

Verification / Alternative check:
The improved sentence "I think she will come to the party." reads smoothly and expresses the idea in standard English. It follows the familiar pattern "I think + clause", which is widely used in spoken and written language and appears in grammar books as the standard structure for expressing opinions.

Why Other Options Are Wrong:
Option A: "So I think she will come to the party." changes the sentence into a different structure where "So" connects to a previous idea and is not directly improving the given faulty sentence. Option B: "I am thinking she will come to the party." is grammatically possible but sounds unnatural for a simple, settled opinion and is not the expected exam answer. Option D: "No improvement" is incorrect because "I think so she will come to the party." is not standard English usage.

Common Pitfalls:
Learners sometimes overuse the word "so" in English due to influence from their first language or from phrases like "I think so". It is important to remember that "I think so" stands by itself, while "I think she will come" directly states the content of the thought. Confusing these patterns leads to sentences that sound odd to native speakers.

Final Answer:
The correct improvement is I think she will come to the party.