Serene means calm, peaceful, and untroubled; hence “Calm” is the best synonym.

Past Perfect shows a completed action before another past action: “had finished” before “arrived.”

Obvious means clear; its opposite is “Hidden,” something not easily seen.

Future Continuous = will be + V-ing (“will be going”).

Polyglot specifically means someone who can speak many languages.

Capable of is the correct collocation.

In reported speech, past continuous commonly backshifts to past perfect continuous.

Indian/British English: “manoeuvre” is correct; AmE uses “maneuver.”

Precise means exact and accurate.

Standard plural is “Phenomena” (Greek origin).

Present continuous passive = is/are being + past participle.

Use “since” with a starting point in time: “since morning.”

Seismologist studies earthquakes/seismic waves.

Benevolent = kind/charitable; opposite is “Cruel.”

After “has,” use past participle “gone,” not “went” (simple past).

Present Perfect Continuous = has/have been + V-ing.

European starts with /y/ consonant sound; use “a.”

Diligent = hardworking; opposite is “Lazy.”

Reluctant means unwilling/hesitant.

For quantity, comparative of “little” is “less” (superlative “least”); “lesser” is attributive, not pure quantity.

Will → “would” and “tomorrow” → “the next day” in reported speech.

Traditional Latin plural is “cacti” (though “cactuses” is also accepted).

Privilege is the correct spelling.

Through indicates means/method: success through hard work.

Cartographer = map maker.

Contract means to shrink; opposite of “expand.”

Use “does not” + base verb: “does not like.”

Obsolete = outdated, no longer in use.

Future Perfect Continuous = will have been + V-ing.

Present continuous passive = is/are being + past participle.