Question obsidi
3.2 Form, Structure, and Sense - Logical sentence placement
0:00
Obsidian is a kind of volcanic glass formed when lava cools so quickly that the atoms inside it cannot arrange themselves in a crystalline structure. You blank more about obsidian’s structure, which is classified as amorphous, in a later chapter.
Which choice completes the text so that it conforms to the conventions of Standard English?
A.
had learned
B.
had been learning
C.
will learn
D.
have learned