The correct answer is D. If I don't sleep well tonight, then I will be tired tomorrow.
Conditional statements are statements that express a relationship between two conditions or events.
They typically follow the form of "if...then..." or "only if...then...".
Option A, "Sleeping well allows me to have the energy I need," is a causal statement, explaining the reason for something. Option B, "I am tired today," is a simple declarative statement. Option C, "I didn't sleep well last night," is a past tense statement of fact.
Option D, "If I don't sleep well tonight, then I will be tired tomorrow," is a conditional statement because it expresses a relationship between two conditions: "if I don't sleep well tonight" and "I will be tired tomorrow." It suggests that the condition of not sleeping well tonight will cause the condition of being tired tomorrow.
Therefore, option D is the only example of a conditional statement among the given choices.