请你根据所学的知识，回答下列问题：光在同种______介质中沿直线传播；在探究凸透镜成像的规律的实验中，在光屏上出现的烛焰的像______实像（选填“不一定是”或“都是”）；当你走近竖立的平面镜时，你通过平面镜所成像的大小______（选填“变大”、“变小”或“不变”）；光能在真空传播，声音______（选填“能”或“不能”）在真空中传播．
①光在同种均匀介质中沿直线传播，光在不均匀的介质中不沿直线传播；
②因为实像可以在光屏上承接，而虚像则不能，所以在光屏上出现的烛焰的像都是实像；
③平面镜成的像与物是等大的，故像的大小取决于物体自身的大小，与物体离平面镜的远近都无关，故不管你走近竖立的平面镜还是远离平面镜时，你通过平面镜所成像的大小不变．
④声音的传播需要介质，可以在固体、液体和气体中进行传播声音，但在真空中不能传播声音．
故答案为：均匀；都是；不变；不能．
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