The type of volcanic material that may plug a volcanic vent ...

[olgavictoria]

The type of volcanic material that may plug a
  volcanic vent causing a buildup of pressure that
  can result in an explosive eruption is composed
  of
  a) high-pressure gases.
  b) low-silica lava.
  c) high-silica lava.
  d) volcanic bombs.

Question 2

The molten rock material that originates far below
  the surface of Earth is called
  a) magma
  b) limestone
  c) feldspar
  d) tephra

[bitingbit]

Answer to Question 1

c

Answer to Question 2

a