Although it was raining, sheila stopped to the puppy who had fallen into the deep hole.
what is the structure of this sentence?
a) complex
b) compound
c) compound-complex
d) simple
explain it so i can understand.

The structure of above sentence is complex.  

Option A

Explanation:

When a sentence consists one independent clause and one or more subordinate clause is said to be a complex sentence. In the above sentence, ''Sheila stopped to help the puppy'' is the independent clause which can form a simple sentence by itself. ''Although it was raining and who had fallen into the deep hole'' are the dependent clauses that does not form a simple sentence by itself.

These two clauses connected by relative pronouns or adverbs are the examples of complex sentences. We can combine them together to get a complex sentence.

- "a nonrestrictive clause functions as a modifier to a noun (that is an object, person or concept). these clauses can be described by the following three options: it is set off by comas, it contains a subject and a verbs and it adds nonessential information to the sentence.

for example, in "here is bill gates, who confounded microsoft software company" we can identify "who confounded microsoft software company" as a nonrestrictive clause modifying the noun bill gates. this clause can be describes as a nonrestrictive clause because it is separated by a comma, it adds nonessential information to identify who bill gates is and it must contain both a subject (who) and a verb (confounded)."