GRE

A few programs may require GRE/GMAT scores but submitting an English language score including IELTS, TOEFL or MET is mandatory. 

Harvard University generally does not publish specific GRE cut-off scores for its programs. Instead, they use a holistic review. However, for MS admission in Harvard, you need to score between 155 to 170 for Verbal and Quantitative, and 4.0-5.0 for Analytical Writing.

Beyond USA, GRE scores are widely accepted for graduate programs in over 90 countries. Top study destinations like Canada, United Kingdom, Australia, Germany, Singapore, France, and the Netherlands. Many universities in these countries ask for the GRE scores at the time of Master's, PhD, and MBA admissions. Always check specific university requirements.

The best GRE syllabus books are ETS Official Guide, Manhattan 5-lb Book, and Kaplan's GRE book. They cover almost everything you need. Practicing with these books can boost the prepration level.

You need to keep few things in mind at the time of buying GRE books such as:

• Official Content: Prioritize ETS study materials or reputed publishers.
• Clear Explanations: Concepts mentioned in books should be easy to understand.
• Practice questions: Choose the books with more pratice question. Also, it should be detailed answer explanations.
• Up-to-Date Content: Pick only the latest edition books which reflecting the current test format.
• Reputation: Check reviews from other test-takers.

It totally depends on the authenticity of your free online study materials. If it is from official website or any reputed publishers, then it is valuable. It will be smart decision if you use both.

Here are some of popular books which offer practice tests for students

• Official GRE Mentor Prep Course by ETS
• POWERPREP Online by ETS
• POWERPREP PLUS Online by ETS
• Kaplan GRE Prep Plus
• The Princeton Review GRE Premium Prep

All these books have good reviews by students as it offers lessons, contents and quizes related to th GRE.

Yes, there are many preparation books come with GRE practice test sets. If you will buy online edition of such books you will get access to online pracice tests with computer adaptive simulations. It is suggested to use official guide and study material by ETS for getting access to ETS's POWERPREP software.