Fill in the blanks with correct preposition:
Napoleon had genius ____ military tactics, without doubt he is genius ____ Mathematics.

Question

Accepted Answer

Here's a detailed explanation for why Option 4 is correct and why the others are not:

**Justification for Option 4 (for, in):**

1.  **First blank: "Napoleon had genius ____ military tactics" - Use of "for"**
    *   When we talk about a natural aptitude, a special talent, or an exceptional ability for a particular skill, activity, or field, the preposition "for" is commonly used with "genius."
    *   "Genius for something" means having an extraordinary natural ability or talent in that specific area.
    *   Examples: "a genius for music," "a genius for invention," "a genius for organization."
    *   In this context, Napoleon had an exceptional natural talent *for* military tactics, making "genius for military tactics" the most appropriate and idiomatic choice.

2.  **Second blank: "without doubt he is genius ____ Mathematics." - Use of "in"**
    *   When referring to exceptional intelligence, skill, or proficiency within a specific academic subject, discipline, or field of study, the preposition "in" is typically used with "genius."
    *   "Genius in something" means possessing profound intelligence or skill *within* that subject.
    *   Examples: "a genius in physics," "a genius in literature," "a genius in computer science."
    *   Here, Mathematics is an academic subject, and stating he is "genius in Mathematics" correctly conveys his extraordinary ability or intelligence within that subject.

Therefore, the combination of "for" (for natural aptitude/talent in a skill) and "in" (for proficiency/intelligence in an academic subject) makes Option 4 the most fitting and grammatically correct choice.

**Explanation for why other options are incorrect:**

1.  **Option 1: in, for**
    *   **"in" for military tactics:** While "genius in" can sometimes be used for a field, "for" is generally preferred to emphasize a natural aptitude or talent for a specific skill or activity like military tactics.
    *   **"for" for Mathematics:** "Genius for Mathematics" is less common than "genius in Mathematics" when referring to proficiency within an academic subject. "In" is more standard for subjects.

2.  **Option 2: at, in**
    *   **"at" for military tactics:** "Genius at" is possible, often implying performance or skill in a specific task (e.g., "good at math," "skilled at chess"). However, "genius for" more strongly conveys the inherent, natural talent or aptitude for a broader skill like military tactics.
    *   **"in" for Mathematics:** This part is correct, as "genius in Mathematics" is appropriate for an academic subject. However, the first preposition makes this option less ideal than Option 4.

3.  **Option 3: in, at**
    *   **"in" for military tactics:** As discussed, "for" is generally a better fit for natural aptitude in a skill.
    *   **"at" for Mathematics:** While one might say "good at math," "genius at Mathematics" is less idiomatic than "genius in Mathematics" when referring to profound intelligence or skill within the academic discipline itself. "In" is the more standard preposition for subjects in this context.