So commonly comes before an adjective or adverb, while such introduces a noun phrase. With a singular countable noun, the pattern is such a or such an. Choose the matching structure.
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Fill in each blank with so, such, or such a.
1. Your sister is pretty.✓
2. She is pretty girl.✓
3. They are brave.✓
4. Your brothers are gentlemen.✓
5. Why do you say things?✓
6. Why would you say thing?✓
7. Why are you always tired?✓
8. He is great writer.✓
9. How do you know people?✓
10. How did you learn to speak English well?✓
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Grammar reviewSo, such, or such a?
Use "so" before an adjective or adverb, with no noun after it: “That movie was so boring.”, “He finished the race so quickly.”
Use "such" before a plural or uncountable noun (no "a"): “I've never heard such excuses.”
Use "such a" before a singular countable noun: “That was such a surprise.”
Notice the difference between those last two: same idea, but excuses is plural (just "such"), while surprise is singular (needs "such a"). That's the whole rule: check whether the noun after it is singular or not.