日本語 Japanese Ask Questions Thread 6

If you have a question about the language, ask it and fellow 4channers might see it and answer it for you.

Japanese - Ask questions thread
http://dis.4chan.org/read/lang/1174719097/1-40

日語 Japanese Ask Questions Thread2 質問
http://dis.4chan.org/read/lang/1206158123/1-40

日本語 Japanese Ask Questions Thread 3
http://dis.4chan.org/read/lang/1267485093/1-40

日本語 Japanese Ask Questions Thread 4
http://dis.4chan.org/read/lang/1302350850/1-40

日本語 Japanese Ask Questions Thread 5
http://dis.4chan.org/read/lang/1330050873/1-40

So I got this sentence from Jishou: その火山は今年２度噴火した。

However I have no idea how to pronounce 度. Rikaichan gives me either たび　or たんび for 'time; times', so if it's this one, how do I choose? However, it also gives 'ど’ for the counter for occurences.

I'm most interested in finding out how to figure these out on my own, if there's a method other than having seen it a billion times, though the answer would also be great, thanks.