user73626: I was reading this GitHub book on Bitcoin
They state that "True or False: Only UTXOs can be used as inputs to transactions."
Is the answer, True because you can only spend what you have. 
Or False, you can out a spent output in the transaction as input, but the network or the miner will reject it.

user208: This question makes no sense.
Of course you can make an invalid transaction that doesn't spend an unspent output. If you're fine with calling invalid things transactions, I could just take a piece of random data and call it a transaction.
A valid transaction can only spend unspent outputs.

73626: <p>I was reading this <a href="https://github.com/decentralisedkev/DecentralisedBookRepo/blob/master/decentralised-technology/terminology/deep-dive-utxos.md" rel="nofollow noreferrer">GitHub</a> book on Bitcoin</p>

<p>They state that "True or False: Only UTXOs can be used as inputs to transactions."</p>

<p>Is the answer, True because you can only spend what you have. </p>

<p>Or False, you can out a spent output in the transaction as input, but the network or the miner will reject it.</p>
 208: <p>This question makes no sense.</p>

<p>Of course you can make an <em>invalid</em> transaction that doesn't spend an unspent output. If you're fine with calling invalid things transactions, I could just take a piece of random data and call it a transaction.</p>

<p>A <strong>valid</strong> transaction can only spend unspent outputs.</p>
