Perhaps you should try some spelling variations:
"canh may va hoc viet nam" » "canh tay va hoc viet nam", "mang may va hoc viet nam", "anh mau va hoc viet nam", "canh may vi hoc viet nam"
"hanh may van hoc viet nam" » "hanh ma van hoc viet nam", "hanh mau van hoc viet nam", "hanh ngay van hoc viet nam", "hanh may san hoc viet nam", "hanh mai van hoc viet nam", "hanh may van hoa viet nam", "hanh may vin hoc viet nam"
"canh day va hoc hien nam" » "canh tay va hoc hien nam", "canh dan va hoc hien nam", "lanh dao va hoc hien nam", "canh day va hoc phien nam", "canh day va hoc hien nay", "canh day va hoc vien nam"

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• Performing a fuzzy search may retrieve terms with similar spellings: (((("canh may va hoc viet nam") or ("hanh may van hoc viet nam"))) or ("canh day va hoc hien nam"))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("canh may va hoc viet nam") OR ("hanh may van hoc viet nam"))) OR ("canh day va hoc hien nam")).
• Removing quotes may allow a broader search: (((( canh may va hoc viet nam ) or ( hanh may van hoc viet nam ))) or ( canh day va hoc hien nam )).
• Adding a wildcard symbol may retrieve word variants: (((("canh may va hoc viet nam") or ("hanh may van hoc viet nam"))) or ("canh day va hoc hien nam"))*.