International students are allowed to work for the university they study at or for a business at the school. But the business must directly provide a service for students. You could work at the bookstore, for example, but not for a company that is building something at the school. Also, a foreign student cannot take the place of an American in a job. International students can work 20 hours a week while having classes; more during school breaks. You can work until you finish your studies. International students normally cannot take a job that has nothing to do with their school. But the government may give permission if students are suddenly faced with difficulties. Examples include large medical bills, the shortage of financial   aid or an unexpected change in the financial support. Students must also meet other conditions  . They must have studied at their American school for at least one year. Students must ask for permission again after a year if they want to continue an off-campus   job. International students who will be studying at graduate school can apply   for some jobs before they come to the United States. A good example is a university job like a teaching or research assistant. Some schools pay their assistants. Others provide free education in return. Many do both. Graduate assistants might teach, give tests, grade work, help with research and clean the offices. Many universities now provide language training for foreign teaching assistants to help them improve their English. Some schools ask foreign students to pass an English speaking test before they are allowed to teach. International student offices at schools have to provide information on students each term for the Department of Homeland Security. Students who _ visa   rules -- for example, by working off-campus without permission -- could be sent home. What can we learn according to the passage?
All the international students can work for large companies. International students are able to work whenever they like. International students may be allowed to work outside the school when having financial trouble. International students must have studied at their American school for less than a year to get a job.