Susan has been urging me to join the …

Analyze the question: You are asked to pick the correct name of an organisation to complete the sentence: "Susan has been urging me to join the ..............."

Concept: The organisation is called the Girl Guides (also known as Girl Guiding or the Girl Guides Association). Here the word "Girl" works like an adjective describing the type of Guides, so it stays singular. "Guides" is plural because it refers to the whole group or movement, in the same way we say "the Boy Scouts" and not "the Boys Scouts."

Step-by-step solution:

1. Option B, "Girls Guide": the noun "Guide" is singular, so it cannot name a group you join. The form is also wrong.
2. Option C, "Girl Guide": this names one member, not the organisation. You can say "She is a Girl Guide," but "join the Girl Guide" sounds incomplete, because the organisation is the plural body.
3. Option D, "Girls Guides": this is wrong because "Girls" should not be plural when it acts as a modifier. Compare "Boy Scouts," "Girl Guides," and "Boys' Brigade," which is a special case with a possessive.
4. Option A, "Girl Guides": this uses the singular modifier "Girl" with the plural "Guides," which is the accepted name of the organisation.

Answer: A. Girl Guides.

Tip: When a noun modifies another noun, it usually stays singular (a shoe shop, a car park, a Girl Guide). The second noun takes the plural when you mean the group, so "the Girl Guides" is the whole organisation.