This question tests your understanding of gerunds and infinitives in English grammar. The sentence structure requires two specific grammatical forms to be correct.

The first blank is the subject of the sentence. A subject is typically a noun or a noun phrase. In this case, the action "to have a horseshoe" is the subject. When a verb acts as a noun, we use its gerund form (the -ing form). Therefore, "Having" is the correct choice for the first blank.

The second blank follows the verb "is supposed". Certain verbs and phrases, like "is supposed to", are followed by the infinitive form (to + base verb). The phrase "is supposed to" indicates an expectation or belief. Therefore, "to bring" is the correct form for the second blank.

Step-by-Step Solution:

Step 1: Identify the subject of the sentence. The subject is the thing that "is supposed" to do something. The action "have a horseshoe" needs to be a noun, so we use the gerund "Having".

Step 2: Identify what follows the phrase "is supposed". This phrase must be followed by an infinitive ("to" + verb). Therefore, the correct form is "to bring".

Final Answer: The correct option is Having / to bring.

The complete sentence is: Having a horseshoe on the door is supposed to bring good luck.

Related Topics & Theory

Gerunds: A gerund is a verb form ending in -ing that functions as a noun. It can be the subject or object of a sentence.
Example: Swimming is good exercise. (Subject)

Infinitives: An infinitive is the base form of a verb preceded by "to" (e.g., to run, to eat). It often follows certain verbs and adjectives.
Example: She wants to leave. (Object)

Verb Patterns: Many verbs and phrases have specific patterns for what follows them. "Is supposed to" is a fixed phrase that is always followed by an infinitive verb.

Key Formulae/Rules

• Subject of a sentence: Use a Gerund (-ing form).
• After the phrase "is supposed": Use an Infinitive (to + base verb).