Questions

ROM cannot be used as stack because it is not possible to write to ROM.

Yes, you are requested to write an essay as part of your TOEFL iBT exam. There are 5 major types for TOEFL essay topics. They are:

1. Agree or Disagree

2. Preference

3. Description / Explanation

4. If / Imaginary

5. Compare & Contrast

The best way to prepare for this essay writing is to understand the writing style clearly. To understand the the genre, you can refer some sample essays submitted before by different contestants. You can get such sample TOEFL essays from various sources such as TOEFL training websites, cheap essay writing service sites, online libraries, etc. Once you are well aware of the writing pattern the next thing is to practice writing random essays. Keep in mind that you should practice writing essays of all above mentioned 5 types. If you make it a routine to write random essays, gradually you can compete at higher level to write the given essay topic for your TOEFL iBT exam.

The clotting of blood is a chain reaction initiated by the enzyme thrombokinase produced by the platelets. This causes prothrombin to be converted into thrombin in the presence of Ca++ion.

Thrombin combines with fibrinogen  to produce fibrin threads which entangles the corpuscles to form the clot.