A compound word is formed with two words, to create a new word.
Option B: 'Star' forms a compound word with 'gazing': stargazing.
'Stargazing' means 'to observe the stars'. Hence option B is correct.
Options A, C and D: 'Goat', 'boy' and 'land' do not form compound words with 'gaze'.
The word 'goatazing', 'boygazing' and 'landgazing' do not exist in standard English language. Hence, options A, C and D are wrong.