There has already been lots of research looking at whether long-distance travel, particularly air travel, increases your risk of a blood clot forming.
到现在为止，已经有很多研究对长途旅行，尤其是空中旅行是否会增加血凝的形成进行探讨。
2
The head's distance from the screen and position in relation to it are also important risk factors.
头部和屏幕之间的距离以及两者之间的方位关系同样是重要的风险因素。
3
New routings of long-distance bird migrations, brought about by new man-made water impoundments, represent an important yet still untested risk of introduction of arboviruses into new areas.