This question tests your understanding of verb patterns after certain verbs and prepositions in English grammar.

The sentence structure is: "I'd intended _____ on you but was prevented from _____ so."

Step 1: Analyze the first blank
The phrase is "I'd intended _____ on you". "Intend" is typically followed by the infinitive form (to + verb). Therefore, we need "to call".

Step 2: Analyze the second blank
The phrase is "prevented from _____ so". After the preposition "from", we need the gerund form (verb + ing). Therefore, we need "doing".

Final Answer: The correct words to fill in the blanks are to call and doing.

The complete sentence reads: "I'd intended to call on you but was prevented from doing so."

Related Concepts

Verb Patterns: Many verbs in English are followed by specific structures. "Intend" falls into the category of verbs that are followed by the infinitive (to + verb). Other examples include: want, plan, hope, decide.

Prepositions + Gerund: Prepositions (like from, of, about, at) are always followed by a noun or a gerund (the -ing form of a verb acting as a noun). The structure "prevented from doing" is a fixed phrase.

Key Formulae/Rules

Rule 1: Verb + to-infinitive
Subject + intend / want / hope / decide + to + base verb
Example: I intend to visit soon.

Rule 2: Preposition + gerund
Subject + verb + preposition + (verb-ing)
Example: She was stopped from leaving.