Answer:
They each have a reading that repeats a sound.
九 KYUU, KU, kokono(tsu) - nine
進 SHIN, susu(mu), susu(meru) - advance, progress
懸 KEN, KE, kake(ru), kaka(ru) - hang, offer, give
快 KAI, kokoroyo(i) - pleasant, delightful
薦 SEN, susu(meru) - recommend, advise, offer