呢份試卷係咪出得唔係咁好？

You are correct.

This actually sounds better:

You have received a letter from your brother, Andy, who is studying in the U.S., telling you he has taken up motorbike racing as a hobby.

(America is not a location. So it is rarely used in expressing a location.)

2015-05-13 08:21:47 補充：
America can mean South America as well.

If used within the U.S., then America works.

However, if outside, it is better to be clear than ambiguous.

2015-05-13 13:43:07 補充：
This is a reference of "America" under Wikipedia:

http://en.wikipedia.org/wiki/America

Remember - it is about presenting a fact clearly. So in this case, the U.S. is more suitable than America.

我認為用 in America 或 in the U.S. 都可以，用 in America 並無 ambiguous ，google search 下就知，唔少用出名傳媒都有用 in America 並表示在美國

2015-05-13 14:55:56 補充：
就連美國總統奧巴馬都有咁講，佢話：The church contains in full the kindness and cruelty, the fierce intelligence and the shocking ignorance, the struggles and successes, the love and yes, the bitterness and bias that make up the black experience in America.

https://www.youtube.com/watch?v=zrp-v2tHaDo

'America can mean South America as well.'
I beg to differ.

When people are referring to the specific continents, we say 'South America' or 'North America', or 'Latin America' when talking about that part of the region politically.

2015-05-13 10:54:06 補充：
This is Wiki's reference to USA.

The United States of America (USA), commonly referred to as the United States (U.S.) or America, is a federal republic consisting of 50 states and a federal district

http://en.wikipedia.org/wiki/United_States

Gary:
Your sentence is correct.

I beg to differ.

America ~ a name commonly used for the US, especially in spoken language
America = 美國 (Yahoo Dict.)

"America’s Most Challenging High Schools" ~ "Washington Post"
America's 當然指美國

http://www.learnersdictionary.com/definition/america

2015-05-13 02:48:34 補充：
"Our father, who is standing near the heavenly gate, is smoking a pipe."
"我們的父親，誰是站在天門附近，抽著煙斗"
~ Google translate 翻譯到唔湯唔水

heavenly gate = 天堂門口 ??
or Tiananmen (天安門) ~ wild guessing

What is "heavenly gate"?

2015-05-13 02:54:17 補充：
nursing nurse? 有無 engineering engineer?
倒不如說 mursing sister (ward sister, floor sister) sister 的 title 高級過普通的 nurse

TOMING88, your writing gives us the benefit of the doubt.

Senior nursing officer ( 舊時英式叫 matron) 是管所有醫院的 sisters

2015-05-13 19:46:10 補充：
Many people from South America dislike the use of "America" to mean just US, but it is very common elsewhere.
尤其 "American" 這個字
American foorball, American girl, American tourist
American tourist may be someone from South America ~ ambiguous?

2015-05-13 19:48:13 補充：
我印象中讀 Geography, America 包括 North America, Central America 和 South America
南美 is also called Latin America
言及 a particular country, 多數在 official documents 例如填 forms, Country of birth 填 USA
國際比賽 US 對 ,,,,,,
其他國家的普羅大眾 spoken English 經常用 America 代替 US

2015-05-13 19:55:26 補充：
"America

English speakers outside North America usually call the United States 'America' and its inhabitants 'Americans.'"

~ from 'New Fowler's Modern English Usage' 3rd edition

Re:-defining (grammar)of relative clauses explaining which particular person you are talking about means there are many Andy, but restricted to the usa one'
there are many films, but restricted to the best;
there are many sisters,but restricted to the nursing nurse.

With non-defining adjective clauses:-
Or non-restrictive rel.clause,it is used to give extra information about him.:-
In reality one Andy, hence:-
Andy, who is studing in Am., telling you he has taken up motorbike as a hobby.
With the two commas used and the adj clause,it is used to qualify Andy.giving extra information,and An appropriate response here.
eg:-Our father, who is standing near the heavenly gate, is smoking a pipe.
It is non-restrictive rel.cl. here,giving extra information about him.Almost an aside .Note one Andy, one father.
Yes,two commas are better for Andy here.