Solution:
- Are your new jeans dark or light? (Jeans is a plural noun, so we use 'are').
- I like these green socks. Can I buy them? ('this/these' refers to the socks, which are plural, so we use 'these'. 'it/them' refers to the socks, which are plural, so we use 'them').
- Your clothes are always nice. Who buys them? ('is/are' refers to clothes, which is a plural noun, so we use 'are'. 'it/them' refers to clothes, which are plural, so we use 'them').
Answer: 1. Are, 2. these, them, 3. are, them.