英语翻译Admission also requires undergraduate grades of at least

英语翻译Admission also requires undergraduate grades of at least a B average over the previous 60 semester hours of credit这句话中 a B average over the previous 60 semester hours of credit 我英语还好，准备出国不好不行啊。这句话我其实懂了九层意思，请懂十层的人回答，关键是previous 60 semester hours of credit的“完整意思”。这个不是懂几个单词就行的，还要了解美国的教育制度。