The optimization process and recommendations:

1. Avoid Selecting Unnecessary Columns (query line: 2): Avoid selecting all columns with the '*' wildcard, unless you intend to use them all. Selecting redundant columns may result in unnecessary performance degradation.
2. Use Numeric Column Types For Numeric Values (query line: 26): Referencing a numeric value (e.g. 4) as a string in a WHERE clause might result in poor performance. Possible impacts of storing numbers as varchars: more space will be used, you won't be able to perform arithmetic operations, the data won't be self-validated, aggregation functions like SUM won't work, the output may sort incorrectly and more. If the column is numeric, remove the quotes from the constant value, to make sure a numeric comparison is done.

The optimized query:

SELECT
        question.*,
        subject.title AS subject_title,
        region.title AS region_title,
        topic.title AS topic_title 
    FROM
        question 
    LEFT JOIN
        subject 
            ON (
                question.subject_id = subject.id
            ) 
    LEFT JOIN
        region 
            ON (
                question.region_id = region.id
            ) 
    LEFT JOIN
        topic 
            ON (
                question.topic_id = topic.id
            ) 
    WHERE
        (
            (
                question.subject_id = '4'
            )
        ) 
    ORDER BY
        rand1 DESC LIMIT 20