problem with .fbx file

Hi everyone
so i have a problem with an object that i made in blender and I want to use it in unity
it’s a human body and as you can see it looks perfect in blender

but when I export it in .fbx and then import it into unity, it will become like this

and as you can see, there are some parts missing specially in legs and i have no idea what is the problem and i’m kinda noob to unity and blender so I would be really happy if you could answer simple

It looks like the problem are inverted normals. Basically, a face in Unity is only visible from one side whereas blender by default shows both sides. Most likely you have some faces facing inwards, which makes them invisible from the outside. Select the missing parts in Blender (they should have a slightly different color) and use Mesh->Normals->Flip Normals.