Topic: Synonyms, Subject: English Grammar (ইংরেজি গ্রামার)

Best Answer Explained in Below-:

The term "sanguine" is derived from the Latin word "sanguis," which means blood. In contemporary usage, it describes a temperament characterized by cheerfulness, optimism, and a confident outlook, especially in challenging situations. The essence of being sanguine involves maintaining a positive attitude and hopefulness about the future, regardless of current difficulties.

Option A, "depressed," is the direct opposite of sanguine, as it denotes a state of unhappiness or despondency. Option B, "unpolluted," refers to cleanliness or purity, which does not relate to emotional or psychological states. Option C, "sinking," implies decline or failure, again contrasting the upbeat nature of being sanguine.

Thus, option D, "optimistic," perfectly encapsulates the meaning of sanguine, as it reflects a hopeful and positive viewpoint, one that expects good outcomes. This positive disposition in the face of adversity is why "optimistic" is recognized as the correct synonym for "sanguine."