Answer:
I got a new puppy because I have been responsible lately.
Step-by-step explanation:
Subordinating conjunctions are words used to connect dependent clauses to independent clauses and express the cause-and-effect relationship or a shift in time and place between these clauses.
It's important to know what each subordinating conjunction means.
Sometimes is not a conjunction at all. It is an adverb.
In the second sentence, there is no conjunction.
If is a conjunction used to introduce the condition necessary for the event described in the independent clause to take place. The third option is incorrect because the events have already taken place. A correct option would be: I will get a new puppy if I am responsible.
Because is a conjunction used to express a cause-and-effect relationship between the subordinate and independent clause. This is the only correct option. Why did I get a new puppy? Because I have been responsible lately.