Read the sentences and say what is not true.

Solution:

We need to read the sentences and identify which ones are not true based on general knowledge or context, and then provide the correct statement.

1. Tom will have his birthday soon. - Tom won't have his birthday soon. (This is a correction of a potentially false statement).
2. Nina will go to Kamchatka next year. - Nina will go to Kamchatka next year. (This statement is presented as true).
3. Nick will catch a big fish soon. - Nick will catch a big fish soon. (This statement is presented as true).
4. It will be sunny tomorrow. - It will be sunny tomorrow. (This statement is presented as true).
5. I think Oleg will buy a new mobile phone. - I think Oleg will buy a new mobile phone. (This statement is presented as true).

Note: The task is to identify what is *not true*. In this case, the first sentence is presented with a correction, implying the original statement 'Tom will have his birthday soon' might be considered false in the context of the exercise, and the provided correction 'Tom won't have his birthday soon' is the true statement.