</p> 23 Paragraph 2 .$ b6 _6 c, ~6 b4 }
24 Paragraph 3 ., j# M" t! i$ ]1 Q+ H0 i
25 Paragraph 4 .9 F- n8 K: |) x% ]& W! h& g5 ?
26 Paragraph 5 .
9 R5 s" Z2 R2 c* J) Z/ B A Study of Sound
$ S0 J6 W/ P- Y' O. q+ @8 { C# w B Highway Police
" c" i- W, ?# O4 v C Working Principles
8 K' Y2 O# y4 S; N0 B2 y D Early Use of "Radar"9 u+ [' o) j) E% d9 y0 n
E Useful Tools( v! b1 b' @8 m9 l+ k2 H
F Discovery by Chance
, m( {$ X8 x' }- Z* O& c- B 27 Echo-sounding devices were early used to .) C# ]/ d" j" J- y3 ]4 t# v3 I
28 Ultrasonic device were used to .5 I; j2 L6 S9 I( J+ L5 f
29 Police use radar on highways to ." W! }3 _. r0 n
30 Radar helps pilots to . w; y9 z7 F$ S# \
A detect nearby objects" p: y1 B. i- G+ q/ ]9 i
B determine the depth of the ocean water( I* x% _- N- _2 v+ `2 K: X5 \- ^
C decide how fast you drive w+ t: c) b1 \5 ?
D stop passing ships
# C2 U& M2 `, P- M1 W E map the ocean floor" e+ J: a& ]- l; N- V- {; l7 Y3 w
F observe water flow |