Fluorescent Bulbs Have Recently Become Much More Efficient Due to the Introduction

Fluorescent bulbs have recently become much more efficient due to the introduction of

A) new types of gases, that glow brighter, within the tube.
B) high- emission phosphor coatings on the inside of the bulb.
C) electronically controlled high- frequency ballasts.
D) longer bulbs.
E) lower density-- i.e., lower pressure-- gases within the tube.