What do you mean with your poll? I will give you some knowledge about bitcoin and blockchain.
BITCOIN Bitcoin is a cryptocurrency, created and held electronically on your PC or in a virtual wallet.
BLOCKCHAIN is a decentralized and distributed digital ledger that is used to record transactions across many computers so that the record cannot be altered retroactively without the alteration of all subsequent blocks and the collusion of the network.

About your question, "How I can invest bitcoin? How can I trust any of the exchange if I invest in them?"
The world is becoming ever more reliant on the internet. So, really: It is no surprise that Bitcoin, a secure, global, and digital currency has claimed the interest of investors. Bitcoin is open to everyone and provides an exciting opportunity to delve into an entirely new asset class. Investing in bitcoin may seem scary, but know that it takes time and effort to understand how Bitcoin works. You should do study and research about the site you want to invest to avoid being scammed.