a. Too heavy to fly, and
b. Could not glide,
why do you suppose that it had bat-like wing membranes between its elongated 5th finger and body?
P.S. Its not 'Brontosaurus', its 'Apatosaurus'...and it had no problem 'lifting its head off the ground', because its neck was reinforced with tendons which kept the neck basically parallel to the ground.....(you might want to rent 'Walking with Dinosaurs'....they did a pretty good job illustrating the most recent wisdom on the subject...)
I'm guessing it flew. It is like a mathematical equation where you have more than one variable. In this case lots of variables, since we do not have a complete creature to test fly and we do not know what the environment was like when it lived.
But the range of possibilities are in two categories:
1. things we don't yet know (or haven't thought about) regarding the animal.
2. Things we don't yet know (or haven't thought about) regarding the environment in which it lived.
The solution to this puzzle could be in one or both categories.
Regarding the Bronto...I mean, Apatosaurus, there is a lot of speculation going on regarding all sorts of things - not just tendons, but blood pressure variances, etc. There's more to it than the pictures in schoolbooks, and people need to be educated about such things.