Hello, I am stuck on this homework sub-questions, c, and d. Could someone please provide me guidance on how to solve this? Also, I answered portion a and b, please help me check if I am doing correctly. Thank you.

Give regular expressions generating the following languages. In all parts the alphabet is {0, 1}

a. {w | w has at least one 1}

Answer: 0*1*

b. {w | w starts and ends with same symbol}

Answer: (0)*U(1)*U0(0)*U1(1)*

c. {w | |w| < 5}

d. {w | every 3rd position of w is 1}