The word "heyday" from the second paragraph can be best expressed by ______.

A．an American team pointed a submillimeter telescope in Hawaii
B．the team used Hubble space Telescope and captured optical images of some galaxies
C．they found five faint old galaxies
D．there are several galaxies in the universe

A．scientists use curtains when doing research on star birth
B．star birth still remains a complete mystery to us
C．scientists are uncovering the mystery of star birth
D．scientists are producing artificial stars in star nurseries