I think the correct answer is either a), or b).
The answer is A. Present progressive
Answer: Subordinate conjunctions do not always have to combine an independent and dependent clauses.
Explanation: Independent clause is a clause that can stand on it's own and be meaningful. Dependent clause can not stand on it's own to give a meaningful idea until it is being combined with an independent clause. We can use subordinate conjunctions to join independent and dependent clauses together but not always. Meaning that, independent and dependent clauses can be joined together without the help of any conjunction word. e.g. I can buy a big house if I have enough money. In this example, we have an independent clause which is "I can buy a big house" and dependent clause which is "if I have enough money". We can see that independent and dependent clauses have been combined together without a conjunction word.
Answer:
It is a pun.
Explanation:
This is because it is a figure of speech that exploits a word's meaning in this case that the book was impossible to put down.
