In the following question, out of the four alternatives, select the alternative which will improve the bracketed part of the sentence. In case no improvement is needed, select "no improvement". Sentence: "Opening the door to her each morning is like (lets) a breath of fresh air into my world."

Introduction / Context:
This sentence improvement question tests your understanding of parallel structure and correct verb forms in English. The sentence compares an action ("Opening the door to her each morning") with another action ("letting a breath of fresh air into my world"). To maintain grammatical and stylistic correctness, both parts of the comparison must use forms that are grammatically compatible and logically parallel.

Given Data / Assumptions:

The full sentence is: Opening the door to her each morning is like (lets) a breath of fresh air into my world.
The phrase "Opening the door to her each morning" is a gerund phrase acting as the subject of the sentence.
The part after "is like" should be a noun or noun-like phrase that can be compared with that gerund phrase.
The bracketed verb "lets" is to be improved or replaced if necessary.

Concept / Approach:
When we use "X is like Y" in English, both X and Y should be similar in grammatical form. Here, X is a gerund phrase: Opening the door to her each morning. Therefore, Y should also be a gerund or noun phrase, not a finite verb. The expression we want is "letting a breath of fresh air into my world", where "letting" functions as a gerund. Using "lets" (a finite verb) after "is like" breaks the structure and makes the sentence ungrammatical. Hence, the correct improvement is to replace "lets" with "letting".

Step-by-Step Solution:
Step 1: Identify the main structure: "Opening the door to her each morning" (subject) + "is like" (linking verb + preposition) + something comparable. Step 2: Recognise that "Opening" is a gerund; the part after "is like" should mirror this nominal form. Step 3: Consider the phrase "letting a breath of fresh air into my world" as a gerund phrase functioning like a noun. Step 4: Check option C "letting" and see that it produces: "is like letting a breath of fresh air into my world", which is grammatical and natural. Step 5: Option A "let" would give "is like let a breath of fresh air", which is incomplete and incorrect in standard English. Step 6: Option B "to let" introduces the infinitive and would give "is like to let a breath of fresh air", which is awkward and not parallel to the gerund "Opening". Step 7: Option D "no improvement" would keep "is like lets a breath of fresh air", which is wrong because "lets" would require its own subject and cannot follow "is like" directly. Step 8: Option E "to have let" introduces a perfect infinitive and changes the time and structure unnecessarily.

Verification / Alternative check:
Read the corrected sentence aloud: "Opening the door to her each morning is like letting a breath of fresh air into my world." The comparison is smooth, poetic, and grammatically sound. If we tried "is like to let" or "is like let", we immediately feel the sentence stumble. Also, standard usage supports gerund after structures beginning with "is like", such as "Life is like driving on a highway" or "Talking to her is like stepping into sunshine." This pattern confirms that "letting" is the right choice.

Why Other Options Are Wrong:
Option A let leaves the phrase without a subject or correct non-finite form; "is like let" is grammatically incomplete.
Option B to let introduces an infinitive that sounds unnatural after "is like" when compared to a gerund subject.
Option D no improvement would keep the ungrammatical "is like lets a breath of fresh air", where "lets" cannot function properly in this structure.
Option E to have let introduces perfect aspect and changes the sense to a completed action, which is not intended and breaks the parallel structure.

Common Pitfalls:
Many learners fail to notice the need for parallelism in comparison structures. They may focus only on tense and ignore the form of the verb. A useful rule is: when a sentence starts with a gerund subject like "Opening the door...", look for another gerund after "is like" or similar expressions. Keeping the same non-finite form on both sides of a comparison makes the sentence smooth, grammatical, and stylistically elegant.

Final Answer:
The bracketed part should be improved to "letting", giving: Opening the door to her each morning is like letting a breath of fresh air into my world.