Undergraduate / Boston U Int. (Experiences with Dad, Confidence, Stock Market) [13]

In British English 'since' has been interchangeably with 'because' for over 100 years. Most of the people in the former colonies use it either way.
Anyway it is not a matter of grammar but semantics or meaning.

Undergraduate / Boston U Int. (Experiences with Dad, Confidence, Stock Market) [13]

Ta that is the short form of thanks in British English.

Undergraduate / (Hardships / Family history / Institution / Qualities) - college essay remake [6]

The first para definetely needs improvement. Make it more real life by alluding to an actual set of circumstances. What you have written is an abstraction.

In paragraph 3 it may, repeat may be an idea to go to the website do some further research and pull out a course, get the details and be able to say 'for example while doing ... I will learn ...'

Undergraduate / Personal statement-Law ("The world makes way for the man...") [4]

You have worked as an intern in a law firm. Bring out your learning with respect to law during that period. Link it to how it further fuelled your desire to work in this field.

Undergraduate / NYU SUPPLEMENT QUESTIONS -- DEADLINE SENSITIVE [4]

This is the para regarding starting a club or an activity. As pointed out 'human rights' is a very wide term and lots of applicants will be pumping it in.

Putting song in your mouth: You could say that you would like to start song groups which sing songs relevant to human rights around the world. A lot of campaigns are accompanied by singing in the local language. This would create a weak link to your next para and make your statement about work for human rights more focused.

Undergraduate / Appeal essay, UC Davis of Engineering [3]

Work on this, the paras can now be shuffled.

To The Appeals Committee / The Dean of Admissions / The Admissions Office (certainly not whomsoever it concerns)
(Read the name of the person/office from which you received the letter allowing you to appeal. Put that reference at the start of this letter. )

I am very appreciate that University of California Davis has given me an opportunity to appeal an adverse admission decision. .

I have been living in the United States for the past three years. I am not a native English speaker. I am working at McDonald's to get more experiences and as I'm working I have learned more English.

I got an A in calculus in Community College during summer. I am good at math and science, and wish to major in engineering at UC Davis. Despite language difficulties I have maintained a GPA of 4.0 in high school.

Given my background I will be adding to the cultural diversity of UC Davis. Besides I have engaged in a lot of volunteer activities to help people.

(Please give examples)

UC Davis is a great opportunity to major in engineering.
(Please go to the website and find something which is good about it. Write that here.)

I am extremely excited at the prospect of learning and contributing at the Universtiy of California Davis.

Thank you very much for your allowing me an appeal.
(Check if it is Univ of Calif Davis or Univ of Calif at Davis.)