The highlighted word means 'Think deeply'.
Option C is correct. The option has the same meaning as the required one. Thus, it is the correct answer
Options A, B and D are incorrect. They do not have the required meaning.
'Sing' means 'Produce tones with voice'.
'Dance' means 'Move in a pattern according to music'.
'Imagine' means 'visulaize' or 'assume'.