For half an hour the glass-bottomed boat drifted. pitching and rolling above the
reef in four- to six-foot waves.
a. fragment
b. run-on
c. correct

There are actually two sentences here.  Because it is not indicated to which sentence you are referring, I will look at both.  

For half an hour the glass-bottom boat drifted.   CORRECT

Pitching and rolling above the reef in four- to six-foot waves.  FRAGMENT

The second sentence is a fragment because there is no subject within the sentence.  Even though it can be determined that what is being pitching and rolling is the boat, sentences should always be considered independently of each other.  Thus, when look at the second sentence we are not told what is doing the action.  As such, it is a fragment.  

explanation:

why r u giving free points

everyday, people all over the world are making sacrifices; all for different reasons. some people may choose to do more simple sacrifices, like, "my daughter is receiving an award at school, but i also have an appointment, so i will decide to cancel that appointment to be there with my daughter" although she is cancelling her appointment, she can easily reschedule it, and spend her time with nore important thungs in life: being there with her daughter. this will make her daughter happy too because she is recieveing an award for her hard work, and it brings us happiness when our hard work is noticed and appreciated.

on the other hand, some people dont know when to make a sacrifice, ir bow to make one. well, making a sacrifice is when you do something for someone else other than yourself, for someone else's happiness, not so you can gain something in return. you do it for them, not for you. so, anyone can make a sacrifice, even the most simplest ones, like giving up the tv for a sibling or a sibling with homework, when you could be doing something else. the point is to others, when you can be doing something else. you do it out of the fact that you want to them, not so that it can benefit you.

making sacrifices benefit people in many ways, it can bring a smile to there face knowing someone is willing to and bring kindess. alot of people tend to feel unwanted and that no one is there for them, but if we show kindess and sacrifice the less importnat things in life for the most important things in life, people will once again feel happiness and more at ease knowing that someone is or was there for them, even if it be only once.

hope this , and let me know if there are any typos, it's hard typing on a phone : )