Which source will be the most effective and credible in answering this research question: What is global warming?

A fact sheet on the government's NASA website

Explanation:

A government website would be an unbiased and credible source

answer

answer: a: they can affect the author’s perspective and in turn the theme and purpose for the writing.

the author's background and time period greatly affect the text that the author produces. this is because we are all a reflection of our time period and background. depending on where and when we were born, we will find some questions more important than others. for example, if we are a wealthy person born in medieval times, we will most likely be interested in courtly love and stories of knights and honour. however, if we are born in the 20th century in africa, we might instead focus on colonialism and its effects on the newly liberated countries. the theme and the purpose of writing are both affected by these conditions.

explanation: