Generally, when "stand" is used to mean "is in a standing position", it is accompanied by a location:
He stood in the corner, sipping a whiskey.
They stood around the table, arguing.
She stood by the window, looking forlornly down the empty driveway.
Often this meaning will be expressed in the past continuous, using "was standing" instead of "stood" to unambiguously refer to the condition of standing, as opposed to the act of standing:
He was standing in the corner, sipping a whiskey.
When "stand" is used to mean "get to one's feet", it is either unaccompanied, or accompanied by an event:
He stood when she entered the room.
They stood as the speaker finished his speech.
"Now that you're here, I can finally leave," she said as she stood.
In my experience, stand up is rarely used for "be in a standing position" when it refers to a person; you are much more likely to hear it used for an inanimate object (especially one which is normally horizontal), and again it will most likely be accompanied by a location:
The bedframe stood up against the wall.
Most often, stand up is used for the action of getting to one's feet:
He stood up and stretched
As I approached, he stood up and reached to shake my hand.
Everyone stood up when the orchestra finished its song.
In your first two examples, people changed from sitting to standing when the president came in, and people changed from sitting to standing for the opening of the speech (they did not remain standing for the entire speech, but sat down again after only a moment or two).
Your given alternatives, "get to one's feet" and "rise", both unambiguously refer to the action of changing from a non-standing position into a standing position.
a) looks OK to me. While 'pass marks' is more idiomatic, 'passing marks' is OK as well.
b) is fine. There's nothing about 'passing her' that implies that they're going through her. One definition of pass is to move by or in front of someone and that's the one intended here.
c) is the one that I would say is incorrect. We don't play 'passing the parcel', we play Pass the parcel.
Best Answer
That is a fascinating question, because at first it appears you are right. Something along the lines of "Prevalence of Overweightness and Obesity" would be correct. However, checking the dictionary, "overweight" can be a noun meaning "weight in excess". All that "overweightness" would be doing is changing an adjective to a noun, and that's apparently not required. Thus, "Prevalence of Overweight and Obesity" is acceptable usage.