How do hot – air balloons work?

Which of these explanations are correct:

1.The balloon acts like a green house, letting the heat from the sun warm the air inside.

2.The burner heats the air inside and the particles move apart , so the air inside is less dense than the cold air outside.

3.The burner heats the balloon fabric which expands, making the volume inside bigger so the air inside is less dense.

4.The air outside gets cooler in the evening, so the balloon rises up.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia).

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