Bee
All bumblebees have two very visible, long antennae and long, ovoid shaped eyes on either side of the head.
Bees will always warn you before stinging, by sticking out one of their legs, if you get too close. Always take care.
Bee-fly
Bee-fly make a bee-like buzz and have a similar furry body, but two tiny antennae and long spindly legs compared to a bee and hoverfly.
Note the long tongue (proboscis) which is as long as their body. They do not sting.
The tongue is permanently extended, unlike a bee and hoverfly which retract their tongues when they have finished feeding.
Hoverfly
Hoverfly have central, short, rather comical antennae and eyes that look like large, snazzy sunglasses.
They do not have the narrow waspish waist like a bee and do not sting.
NOTE: If you have reason to think you may be allergic to bee venom, you should carry an Epipen at all times.