The tomato juice left brown ____ on thefront f my jacket

The fast popularity of cloud computing means netizens will need to take added measures to make sure their data stay __________in the digital age.

Sam ______ some knowledge of the computer just by watching others working on it.

We carefully， but we didn’t anything.

MrSmith wanted to buy the house and he told me that ____the house cost,it would be worth it[ ]