According to Krashen, ______ refers to the gradual and subconscious development of L1 ability by using it naturally in daily communicative context.

A．dinosaurs' geographical location.
B．shifting views of dinosaurs.
C．migration patterns of dinosaurs.
D．geologic activity of Earth.

A．Tyrannosaurus Rex had lips and Triceratops had cheeks.
B．dinosaurs might have looked like mammals such as sheep.
C．dinosaurs might not have looked like what we thought.
D．dinosaurs must have looked like birds or crocodiles.