1. this small island in Southeast Asia is a wonderful andsafe place to take a holiday.
介词in指小岛位于东南亚范围内。例:哈尔滨在中国的北部。
Harbin is in the north of China.

2. On the one hand, more than three quarters of thepopulation are Chinese ...On the other hand,Singapore is an English-speaking country...
一方面，四分之三以上的人口是中国人.…另一方面,新加坡是一个说英语的国家。
(1) One the one hand...on the other hand...一方面……另一方面……;用于表述一个事情的两个方面。
注意:on the one hand中的the可以省略。
例:一方面，你必须努力学习;另一方面，你应该注意身体。
On (the)one hand, you must study hard; on theother hand, you should pay attention to your health.
(2) three quarters四分之三
分数的构成:分子用基数词，分母用序数词，若分子大于1，则分母加s。
例:
1/3one third
2/3 two thirds
1/4 one/a quarter 或one fourth
3/4 three quarters或 three fourths
1/2 a half 或one second