The sentence is ok in response to the question asked. The questioner asks the
responder to give his or her opinion or make a choice, and the responder
indicates his opinion or choice by using the words “I think”, which
function syntactically here in parenthesis and
could have, but don't necessarily need, a
comma after them, so “I think(,) the study of thermal properties.”
Rozumíme nikoliv I think + noun, ale I think (we're going to
perform) the study of … Je to svým způsobem taková “ostřihaná”
věta – a “clipped” sentence.
See Hovorové
“ostříhané” věty (Ellipsis 1).
More examples:
- A: What flavour ice cream do you want? B: I think(,) vanilla.
- A: What do you fancy for lunch? B:| I think(,) salad.
- A: I want to get Lucy a CD for her birthday. What sort of music should
I get? B: I think(,) opera. She's a real opera buff. [Význam
buff2]