Which of the following techniques and/or instruments are used to monitor volcano deformation?
[note: there may be more than 1 correct answer. choose all correct answers for full credit. there is a penalty for selecting an incorrect answer.]

a) direct measurement between 2 points on the volcano

b) insar

c) seismometer

d) cospec

e) ftir

f) acoustic flow meter

g) tiltmeters

h) gps

i picked e, g, and h and got 0.75/1 on the i don't know which is wrong or right, or whether i missed one or not.