During which month do people sleep the least?

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?

A certain street contains 100 buildings. They are numbered from 1 to 100. How many 9's are used in these numbers?

How many sides does a circle have?

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

What are the five permanent members of the UN Security Council?

a) France, Germany, Italy, Japan, United Kingdom
b) Canada, Mexico, Saudi Arabia, Turkey, United Arab Emirates
c) Brazil, India, Nigeria, South Africa, South Korea
d) China, France, Russia, United Kingdom, United States

I get hot but I never sweat,
I cook food but I am not a chef,
I have a door but you can't enter me,
I have a light but I am not a lamp.
Who am I?