Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

Only one color, but not one size,
Stuck at the bottom, yet easily flies.
Present in sun, but not in rain,
Doing no harm, and feeling no pain.
What is it?

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

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

What Word am I Looking For ?

A car is crossing a 20 km-long bridge. The bridge can support at most 1500kg of weight over it. If somehow, the weight on the bridge becomes more than that, it will break.

Now, the weight of the car is exactly 1500kg. At the midway, a bird comes and sits on the roof of the car. This bird weighs exactly 200 grams.
Can you tell if the bridge breaks at this point or not?

There is one thing that goes round the house and also inside the house but never even share a brief touch. What is it?

He runs but never walks. Murmurs, but never talks. Has a bed, but never sleeps. And has a mouth, but never eats?

I am never scared but became petrified and can’t live in a house but would die to make one. What am I?

Which five letter word can be added at the end of below word to form a
valid word?

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There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?