Which of the following sentences about Ms. Praveena showing a documentary film in class today is punctuated and capitalised correctly in standard English?

Introduction / Context:
Questions on correct sentence formation often test punctuation, comma usage, and capitalization rules in English. Here the focus is on a sentence where a teacher, Ms. Praveena, shows a documentary in class and the writer highlights a quoted phrase within the sentence. The learner must identify which option follows standard conventions for commas and capital letters inside a sentence, not at the beginning of a new sentence.

Given Data / Assumptions:
- The base idea is that Ms. Praveena showed a documentary in class today.
- The clause "because the film focuses on a similar subject to a book we are going to read" is a reason clause starting with "because".
- The quoted part is "focuses on a similar subject".
- We assume standard modern English punctuation habits rather than stylistic variants.

Concept / Approach:
We should remember that commas are not placed unnecessarily between a noun and its clause when the structure flows smoothly. Also, capitalization inside quotation marks usually follows the rule that the first word is capitalised only if it begins a sentence or is a proper noun. Here, the quoted phrase appears in the middle of a larger sentence and is not a complete new sentence on its own. Therefore, "focuses" should not be capitalised. We must also avoid putting a comma between "film" and its following clause when "because" already introduces a smooth connection.

Step-by-Step Solution:
Step 1: Check comma placement: there should be no unnecessary comma between "film" and the quoted phrase when the clause flows naturally. Step 2: Check capitalization: words inside quotation marks should not start with a capital letter unless they begin a sentence or are proper nouns. Step 3: Inspect option A: it has a comma after "film," which is unnecessary and interrupts the flow. Step 4: Inspect option C and D: both have "Focuses" starting with a capital F inside the quotation marks, which is incorrect in this mid sentence position. Step 5: Inspect option B: it has no comma after "film" and writes "focuses" with a small f, which matches standard rules. Therefore B is correct.

Verification / Alternative check:
Read the sentence aloud with different options. Option B sounds natural: "because the film focuses on a similar subject to a book we are going to read". There is no awkward pause after "film", and the quoted phrase behaves like a direct highlight of the verb phrase. Options with a comma after "film" introduce an unnecessary break. Options with "Focuses" capitalised feel wrong because the quoted phrase does not start a new sentence; it is just a highlighted part of the existing sentence.

Why Other Options Are Wrong:
- Option A: incorrect because the comma after "film," separates the noun from its clause unnecessarily.
- Option C: contains both the unnecessary comma and incorrect capitalization of "Focuses".
- Option D: even without the comma, it wrongly capitalises "Focuses" inside a mid sentence quotation.
Only option B respects both comma placement and capitalization rules.

Common Pitfalls:
Learners sometimes insert extra commas wherever they sense a pause in speech, but written punctuation follows grammatical structure rather than merely spoken rhythm. Another common mistake is to capitalise the first word inside quotation marks automatically, even when the quoted portion is not a full sentence on its own. Remembering that capitalization depends on sentence structure, not on the presence of quotation marks, helps avoid these errors.

Final Answer:
The correctly punctuated and capitalised sentence is Ms. Praveena showed us a documentary in class today because the film ""focuses on a similar subject"" to a book we are going to read.