One reason would be to prevent bots from coming in and mechanically recommending certain contributors over and over again.
You can only recommend another contributor once because you already trust them - you shouldn't need to trust them more than you already do. This is also because it is to combat vandalism in Trust Points, as you can get a friend to trust you thousands of times so you can get thousands of trust points, and that isn't how you should earn trust points. Thus, only one recommendation per contributor.
Simply click on the 'recommend' link at the bottom of the answer page. You can only recommend a contributor once - and once recommended - you cannot undo the action.
There is no way to recommend an answer mainly because answers can be changed. A once popular answer changed into an un-popular one and vice versa. But if you think an answer is good be sure to recommend the contributor.
Trust points are given by the Readers of your answers. Each member can recommend a contributor once. Answers are counted as contributions.
You can rate an answer - by awarding a trust point to the contributor stated at the bottom of the answer box. You can only recommend each user once though.
you cant
You cannot anymore. The quiz is an old thing where users made their own quizzes. The more quizzes you pass, the more levels you gain. An ancient contributor of the quiz is someone who once did the quiz. Happy Howrsing!
There is nothing against that. One Supervisor once said "We can't trust you if you can't trust yourself".
You cant. The item is a key item and you cant use it more than once
No you cant
The item is a key item
I would recommend ejecting sperm in women not men.