Vocabulary and Synonyms

Credible means believable or trustworthy. Probable is the closest synonym as it relates to something that can be believed or is likely to be true. Fatal means deadly, refuse means to decline, and considerable means significant in amount.

Laborious means requiring considerable effort and hard work. Industrious is the correct synonym as it means hard-working and diligent. Dismal means gloomy, and deceit means lying/deception.

'Mild' means 'calm'.

A hypothesis is a proposed explanation or tentative statement about a phenomenon that can be tested - it's essentially a proposition put forward for investigation. While related to 'assumption' and 'conclusion,' a hypothesis is specifically a testable proposition. 'Fact' is incorrect because a hypothesis is not yet proven.

Lethargy means a lack of energy, enthusiasm, or spirit - a state of sluggishness or inactivity. 'Laxity' means a lack of strictness or care, which aligns closely with lethargy's sense of slackness. While 'listlessness' is also close, 'laxity' captures the quality of being loose or negligent. 'Impassivity' means calmness without feeling, and 'serenity' means peacefulness - both different from lethargy.

Ocular means relating to the eye or vision - it comes from the Latin 'oculus' meaning eye. The correct answer 'pertaining to the eye' is the exact meaning. 'Colossal' means huge (from the Colossus of Rhodes), 'frequent' means happening often, and 'irregular' means not following a pattern.

Palpitation refers to a rapid, strong, or irregular heartbeat that can be felt by the person - essentially the physical sensation of one's heartbeat. 'Heartbeat' is the most accurate synonym. 'Heart attack' is too extreme, 'courage' and 'loyal' are completely unrelated meanings.

Ostentatious means displaying wealth, knowledge, or attractively in a showy manner to impress others. 'Showy' directly captures this meaning of something designed to attract attention through display. The other options (disappear, average, timely) are unrelated to the concept of conspicuous display.

Nebulous means vague, unclear, or ill-defined - literally 'cloud-like' in its lack of definite form. 'Vague' is the perfect synonym, capturing the essential meaning of something not clearly defined. Tiny, insignificant, and inadequate refer to size or importance, not clarity.

Pivotal means of crucial importance, acting as a central point or hinge on which everything turns. 'Crucial factor' captures this essential meaning of something fundamental or decisive. Private, skilled, and provoked are unrelated to the concept of central importance.

Placid means calm, peaceful, and not easily upset or excited. 'Calm' is the direct synonym, capturing the state of tranquility. Clear, enjoyable, and dull don't convey the peaceful nature of placid.

 Obligatory refers to obligation or rather what is required of someone or something; therefore required is the correct choice.

Nocturnal means relating to, occurring, or active at night. 'Pertaining to night' is the literal definition and correct synonym. The other options (about nature, sympathetic, sensible) are unrelated to the time-of-day meaning.