What has many keys but can’t open a single lock?

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

I have four wings but can't fly.
I express no emotions.
I am found on the exact spot every time you look.
I keep toiling away with a little sound.

Do you know what am I?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

One day, John and his friends were playing around. Jacob hit something with a Pin and it popped. John's dad came into the room that very moment, but he wasn't mad. In fact, he was smiling. What did Jacob hit?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

What month of the year has 28 days?

During which month do people sleep the least?

If six children and two dogs were under an umbrella, how come none of them got wet?