The common cold has long been a major puzzle, in large part because there isn't just one type of cold bug.
普通感冒长期以来一直是一个很大的谜团，其主要原因是因为造成感冒的致病原并非只有一种感冒病毒。
The common cold has long been a major puzzle, in large part because there isn't just one type of cold bug.
普通感冒长期以来一直是一个很大的谜团，其主要原因是因为造成感冒的致病原并非只有一种感冒病毒。
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