Present Perfect Passive

Comment on the following examples. Change them into Active Voice.

Think of a proper action doer if it is not mentioned.

Since prehistoric time extraneous substances have been added to food by man.
Oh! The taste has been made more interesting with adding more spices.
A better life has always been searched by mankind.
Physical hazards to health still have not been eliminated at the factory.
Tablets have not been locked away, which is why the child is reaching for the bottle of pills.
A tropical “Brown Widow” spider, new to the Los Angeles area has been found.
Tiny machines such as transistors the size of a single molecule have already been created by new technology.
Look. The steps have been sanded and they are not slippery.
This crockery has always been used on special occasions.
Too many nails have been hammered. Now we have to pull some out.
The picture has been ruined with a hugeblob of paint.
The old house has been pulled down. There is going to be a new car park.
The roof does not leak. It has been mended.
The mirror has been accidentally broken. Will it bring bad luck?
A table for two has already been booked.
It smells delicious. The refreshments have been served.
Has my mountain bicycle been repaired yet?
The neighbour’s home has been broken by burglars.
Look. Your socks have been worn into holes.
The twins have been delivered by Caesarean section.
We have just been warned of pickpockets.