Where is the flaw in this argument?

Okay, so my logic professor is saying that this argument is flawed, but I can't find it. 1) Whatever begins to exist must have a cause for its existence. 2) The universe began to exist (as proven by the Big Bang). 3) Therefore, the universe has a cause. So you test it by asking these questions. 1) Are... show more Okay, so my logic professor is saying that this argument is flawed, but I can't find it.

1) Whatever begins to exist must have a cause for its existence.
2) The universe began to exist (as proven by the Big Bang).
3) Therefore, the universe has a cause.

So you test it by asking these questions.

1) Are the premises true?
2) Does the conclusion follow from them?

The answer to both seems to be yes. If both are true than the argument is not flawed. But my professor keeps telling me I am wrong! So where is the flaw? Is it a fallacy I am not aware of?

It needs to be answered by Friday night; my professor is testing me on it. !! Please help!!
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