I really like the way you used the factor of 7 here. Impressive general knowledge. Did you know all these facts or did you look them up?
They all run/depend on some sort of fuel: sun-hydrogen, car-petrol, candle-wax, electricity-coal, oil, gas, wind, water, solar, etc,...
Here's another relationship using the concept of 'valuable': an elephants tusk is valuable, an antique table is valuable, Elvis's guitar is...
Apologies for the late reply. But Cacian here has got the objective right. You need to find ways in which some or all of the words are related....
Creativity challenge - find relationships between the following words: elephant, guitar, minute, table.
Separate names with a comma.