Please check my answer thanks :)

In the sentence "Although the book was more than 50 years old, it still contained helpful information", the word although is what.

I said it's adjective

It's a subordinating conjunction:

http://grammar.ccc.commnet.edu/grammar/conjunctions.htm
(Scroll down to Subordinating Conjunctions.)

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thanks i understand now :)

You're welcome.

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In the sentence "Although the book was more than 50 years old, it still contained helpful information," the word Although is a(n)

To determine the part of speech of a word, we can look at its function in a sentence. In the given sentence, "although" is used to introduce a subordinate clause that presents a contrasting idea. It does not modify a noun, which is a characteristic of adjectives.

The word "although" is actually a subordinating conjunction. Conjunctions connect words, phrases, or clauses. In this case, "although" connects the subordinate clause ("the book was more than 50 years old") to the main clause ("it still contained helpful information"). Therefore, the correct answer is that "although" is a subordinating conjunction, not an adjective.