Verb conjugation of "joindre" in French

Some idiot copied it from there and inserted it into our vocabulary builder. He is allowed to do it as long as he indicates that sentences where taken from another source and are for self usage only.
The idea is to use the sourcing to get as much information as possible about learning abilities and disabilities in average. This way we can determine and forecast best practices for language learners based on some parameters.
Have you ever visited the U.S. before and if so, where have you been in the U.S.? I've been travelling in California, it was very amazing. We have traveled by car. Here are my corrections.