Rearrange the parts of the sentence in correct order.

One element that

P. is timing, in particular ensuring that

Q. is essential to navigating deep space

R. the time on board spacecraft is synchronised

S. with the time on the ground

QPRS

The correct answer is Option (4) → QPRS

One element that
Q. is essential to navigating deep space
P. is timing, in particular ensuring that
R. the time on board spacecraft is synchronised
S. with the time on the ground