For Question 28, the correct option is **C. join**. The complete sentence would read: "Don't join the music club if you have a love for singing or playing instruments."

For Question 29, the correct option is **A. recycle**. The complete sentence would be: "I think recycle paper and cardboard to help save trees." However, for the sentence to be grammatically correct, a slight modification is needed. A better formulation would be: "I think we should recycle paper and cardboard to help save trees."