Difference between these words What's the difference between these pairs of words? My book doesn't give a clear distinction between them.

如果 - 要是

必须 - 要

报名 - 注册

查 - 检查

读书 - 看书
These are similar terms just as their english counterparts:  

如果 - In case
要是 - If

必须 - Necessary
要 - Need / require

报名 - Sign up
注册 - Register  

查 - Check / Search
检查 - inspection

读书 - Reading (in terms of Studying)
看书 - Read a book