1. Imagine you have a new pen pal from America. Then ask about 4 questions of him.
2. Pretend you have a new pen pal from America. Then ask about 4 questions of him.
3. Suppose you have a new pen pal from America. Then ask about 4 questions of him.
4. Think you have a new pen pal from America. Then ask about 4 questions of him.
(Are all the expressions grammatiacl? Do we have to use 'had' instead of 'have'?)
grammatical? (mistake).....
All are fine except #4. The verb 'think' doesn't work well in this context.
Also, I'd delete 'about' in your sentences. It's not incorrect. It just reads awkwardly.
All four expressions are grammatically correct. However, the choice of verb ("have" or "had") depends on the context of the situation.
1. "Imagine you have a new pen pal from America." - This implies that you do not currently have a pen pal from America, but you are asking the reader to imagine having one. In this case, using "have" is appropriate.
2. "Pretend you have a new pen pal from America." - Similar to the first expression, this also implies that you do not actually have a pen pal from America, but you are instructing the reader to pretend or imagine having one.
3. "Suppose you have a new pen pal from America." - Again, this suggests that you are asking the reader to imagine having a pen pal from America. The word "suppose" indicates that you are presenting a hypothetical scenario.
4. "Think you have a new pen pal from America." - This sentence also suggests a hypothetical situation, but it additionally implies that you are asking the reader to consider or contemplate having a pen pal from America.
So, depending on the context and intention, any of these expressions can be used. If you currently have a pen pal from America, then using "had" instead of "have" would be more appropriate to describe a past tense situation.