In the following question, a sentence is provided with four words marked as (A), (B), (C), and (D). These words may not be in their proper positions. Choose the pair of words that should be interchanged to make the sentence grammatically and contextually correct.

Engaging (A) young students in foster (B) learning through interactive experiments can active (C) their natural (D) curiosity about environmental science.

The correct option is B-C.

Explanation:
Let's analyze the positions of the highlighted words in the given sentence:
• (A) Engaging: Correctly used as a gerund to begin the clause ("Engaging young students...").
• (B) foster: "Foster" is a verb meaning to encourage or promote. In its original place ("in foster learning"), a verb is incorrectly placed where an adjective is needed to describe "learning".
• (C) active: "Active" is an adjective. In its original place ("can active their natural curiosity"), an adjective is incorrectly placed where a base verb is needed after the auxiliary verb "can".
• (D) natural: Correctly used as an adjective modifying the noun "curiosity".

To correct the sentence grammatically and contextually, we need to interchange (B) foster and (C) active:
1. Replacing "foster" with "active" creates the noun phrase "active learning", which is contextually meaningful.
2. Replacing "active" with "foster" creates the verb phrase "can foster", which is grammatically correct.

Corrected Sentence:
"Engaging young students in active learning through interactive experiments can foster their natural curiosity about environmental science."