Passage about "Reading"

When you read something in a foreign language, you frequently come across words you do not (1)_____ understand. Sometimes you check the meaning in a dictionary and sometimes you guess. The strategy you adopt depends very much upon the (2)_____ of accuracy you require and the time at your disposal.

…..

When you come across unknown words in an exam text, it is very easy to panic. However, if you develop efficient techniques for guessing the meaning, you will (3) ____ a number of possible problems and help yourself to understand far more of the text than you at first thought likely.

Two strategies which may help you guess the meaning of a word are: using contextual clues, both within the sentence and outside, and making use of clues (4) ____ from the formation of the word.

1: A. wholly B. fully C. completely D. totally

2: A. extent B. degree C. range D. level

3 A. surpass B. get over C. go over D. overcome

4: A. derived B. extracted C. coming D. originated

The keys are: 1.b, 2. b, 3.d, 4.a. My questions are:

Why can’t we say:

1c. completely understand – What’s the difference between “completely understand & fully understand?;

2. d. level of accuracy – What’s the difference between “degree of accuracy & level of accuracy”?

3. b. get over – get over a number of possible problems instead of “overcome … problems”?

4. c. coming. Is it because we usually say “… word derived from” which means: coming from…