The task requires selecting all numbers that are multiples of 7. Let's verify each number:

• 7: $7 \times 1 = 7$ → Yes, it is a multiple of 7.
• 14: $7 \times 2 = 14$ → Yes, it is a multiple of 7.
• 19: $19 \div 7 = 2.714$ (not an integer) → No, not a multiple of 7.
• 21: $7 \times 3 = 21$ → Yes, it is a multiple of 7.
• 28: $7 \times 4 = 28$ → Yes, it is a multiple of 7.
• 34: $34 \div 7 = 4.857$ (not an integer) → No, not a multiple of 7.

Correct answers:

• 7
• 14
• 21
• 28

Would you like additional clarification or details on multiples?

Here are five related questions to explore:

1. How can you quickly determine if a number is a multiple of another number?
2. What are all the multiples of 7 between 1 and 50?
3. How do multiples relate to factors in mathematics?
4. Can multiples of 7 always be odd, even, or mixed? Why?
5. How do you find common multiples of two numbers, like 7 and 5?

Tip: Multiples of a number are obtained by multiplying it by whole numbers starting from 1.