What goes up but never comes down?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

ENEMY = 2 * LINK
LINK + 2 = HELL

Then what will be TAXI + HELL? Select from the options below:
a) ROTTEN
b) DANGER
c) HEAVEN
4) MORTAL

In a basket of apples,
when counted in twos, there was one extra
when counted in threes, there were two extra when counted in fours, there were three extra
when counted in fives, there were four extra
when counted in sixes, there was five extra.

However, if the apples were counted in sevens, no extra apple was left. Can you calculate the minimum number of apples that were present in the basket?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

You need to pick one entry from pot A and one from pot B to have a perfect match. Can you do it?

I am the beginning of everything, the end of everywhere. I'm the beginning of eternity, the end of time and space. What am I?

First, think of the colour of clouds. Next think the colour of snow. Last, think of the colour of the moon. Now, what do cows drink?

what's the probability of getting a king or a queen from a pack of 52 cards?

I am the one who remains awake when you sleep. But I need to rest when you awake. Who Am I?