S1: This weather-vane often tops a church spire, tower or high building. P : They are only wind-vanes. Q : Neither alone can tell us what the weather will be. R : They are designed to point to direction from which the wind is coming. S : Just as the barometer only tells us the pressure of air, the weather-vane tells us the direction of wind. S6: The weather-vane can, however give us some indication of other. The Proper sequence should be: A. PQRS B. PSRQ C. PRSQ D. SPQR

The correct answer is C. PRSQ.

The first sentence (S1) introduces the topic of the weather-vane. The second sentence (P) states that weather-vanes are only wind-vanes. The third sentence (R) explains that wind-vanes are designed to point to the direction from which the wind is coming. The fourth sentence (S) compares weather-vanes to barometers, which only tell us the pressure of air. The sixth sentence (S6) states that weather-vanes can give us some indication of other weather conditions.

The correct sequence of sentences is C. PRSQ. This is because the second sentence (P) builds on the first sentence (S1) by providing more information about weather-vanes. The third sentence (R) builds on the second sentence (P) by explaining how weather-vanes work. The fourth sentence (S) builds on the third sentence (R) by comparing weather-vanes to barometers. The sixth sentence (S6) builds on the fourth sentence (S) by stating that weather-vanes can give us some indication of other weather conditions.

The other options are incorrect because they do not follow the logical flow of the text. Option A, PQRS, is incorrect because the fourth sentence (S) comes before the third sentence (R). Option B, PSRQ, is incorrect because the sixth sentence (S6) comes before the fourth sentence (S). Option D, SPQR, is incorrect because the first sentence (S1) comes after the second sentence (P).