The antonym of radiance is \_.

Here are the solutions to the questions:

12. The antonym of radiance is _____.

• Radiance means brightness or light.
• Luminance is a measure of brightness, making it a synonym.
• Dullness means a lack of brightness or vividness, which is the opposite of radiance.
• Affluent means wealthy.
• Intricate means complex. The antonym of radiance is dullness.

The correct option is $\boxed{\text{B}}$

13. What is the plural form of the word 'shelf'?

• For nouns ending in -f or -fe, the plural is often formed by changing the -f or -fe to -ves.
• Therefore, 'shelf' becomes 'shelves'.

The correct option is $\boxed{\text{C}}$

14. Identify the proper noun in the following sentence: "Rihan plays tennis exceptionally well."

• A proper noun is a specific name of a person, place, or organization, and it is always capitalized.
• In the sentence, "Rihan" is the specific name of a person.
• "exceptionally" is an adverb.
• "tennis" is a common noun.
• "well" is an adverb.

The correct option is $\boxed{\text{A}}$

15. Complete the sentence by choosing the appropriate option. "While Raj was watering the plants, _____"

• The first part of the sentence, "While Raj was watering the plants," uses the past continuous tense, indicating an ongoing action in the past.
• The second part of the sentence should describe an event that happened during this ongoing action. The past simple tense is typically used for a completed action that occurred within the duration of another ongoing action.
• A) he saw a stranger entering the garden. This uses the past simple tense ("saw") for the interrupting event, which is grammatically correct and natural.
• B) he has seen a stranger entering the garden. This uses the present perfect tense, which does not fit the timeline established by the past continuous.
• C) he was seeing a stranger entering the garden. While grammatically possible, "see" is often a stative verb and "was seeing" is less common for a sudden perception than "saw".
• D) he could have seen a stranger entering the garden. This implies possibility rather than a definite event.

The correct option is $\boxed{\text{A}}$