Please help and explain 18-22!!

18. Which molecule has three 'H NMR signals and will produce the following NMR spectrum? A. CH3CH2CH2CH3 B. CH3C(O)CH2CH3 C. CH3CH2CH3 D. CH3C(O)OH2CH3 19. Which molecule has two 'H NMR signals and will produce the following NMR spectrum? A. CH3COOH B. CH3CH2OH C. CH3CHO D. CH3(O)OCH3 20. Which molecule has two 'H NMR signals and will prodoce the following NMR spectrum? A. CH3COOH B. CH3CH2OH C. CH3CHO D. CH3C(O)OCH3 21. Which molecule has one ' H NMR signal and will produce the following NMR spectrum? A. CH3CH2CH3 B. CH3CH3 C. CH3C(O)OCH3 D. CH3C(O)CH3 22. Which molecule has four 'H NMR signals and will produce the following NMR spectrum? A. CH3C(O)CH2CH2CH3 B. CH3CH2CH2CH3 C. CH3C(O)OCH2CH2CH3 D. CH3CH2C(O)CH2CH3