Final answer:
Entry 2: Sadness and frustration. The writer shows sincerity by conveying their genuine feelings and emotions through their words.
Step-by-step explanation:
The most sincere emotions are demonstrated in Entry 2: Sadness and frustration. The writer shows sincerity by conveying their genuine feelings and emotions through their words. For example, they might use descriptive language to express their sadness or frustration. They could also provide personal anecdotes or experiences to illustrate their emotions, making their writing more honest and sincere.