Learning English seems easy _______, but it is not really easy if you want to learn it well.[ ]

It’s the kind of the music ______ you can dance to .

I ______ my mind to study harder since I visited the Shanghai Supercomputer Centre.

__________ the stars are, the smaller they look, as is known to all the people.

I feel blue these days.—Why? What makes you so _________? Cheer up, please.