
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
In the tetrahedron $S-ABC$, $\angle SBA=\angle SCA=90^{\circ}$, and $\triangle ABC$ is an isosceles right triangle with hypotenuse $AB=a$. Among the following conclusions: 
1. The angle formed by the skew lines $SB$ and $AC$ is $90^{\circ}$.
2. The line $SB$ is perpendicular to plane $ABC$.
3. Plane $SBC$ is perpendicular to plane $SAC$.
4. The distance from point $C$ to plane $SAB$ is $\frac{a}{2}$.

The correct conclusion(s) is/are \_\_\_\_\_\_\_\_

Present the answer in LaTex format: \boxed{Your answer}
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