The Moon, which has undergone a distinct and complex geological history, presents a) n; z! E1 F0 ^7 ^) v7 D1 R
striking appearance. The moon may be divided into two major terrains: the maria (dark 5 ^3 G9 q' |" `& x
lowlands) and the terrace( bright highlands). The contrast in the reflectivity (the capability
6 S4 i% w9 k+ Q. Xof reflecting light ) of these two terrains suggested to many early observers that the two
" f* B6 h+ ^, n- {4 n6 F5 c+ m(5) terrains might have different compositions, and this supposition was confirmed by
9 z4 e. B, C% m" ]2 t" v$ bmissions to the Moon such as Surveyor and Apollo. One of the most obvious differences
6 `; y# ?3 S; o- R" P- kbetween the terrains is the smoothness of the maria in contrast to the roughness of the
# A5 {3 J+ x6 M3 N; M; fhighlands. This roughness is mostly caused by the abundance of craters; the highlands are ; Q3 `. e$ r% ^: m7 `$ c
completely covered by large craters( greater than 40-50 km in diameter), while the craters
, Z; o5 W/ A$ N; y(10) of the maria tend to be much smaller. It is now known that the vast majority of the Moon’s
% I" G9 ~1 t i Acraters were formed by the impact of solid bodies with the lunar surface.- n; d! d' V& ?$ i; ]0 q9 v% @
Most of the near side of the Moon was thoroughly mapped and studied from telescopic
0 t$ v* a P2 }pictures years before the age of space exploration. Earth-based telescopes can resolve
. M) {9 l7 n* v# L' J; @objects as small as a few hundred meters on the lunar surface. Close observation of
! N7 I% d \9 K(15) craters, combined with the way the Moon diffusely reflects sunlight, led to the * v/ |/ E" c' R; G" z& l
understanding that the Moon is covered by a surface layer, or regolith, that overlies the
, s$ {& f+ M5 K" ~6 asolid rock of the Moon. Telescopic images permitted the cataloging of a bewildering array6 Y- s4 n) \4 i7 ~0 v( C
of land forms. Craters were studied for clues to their origin; the large circular maria were
1 x5 N# E5 R6 \- _(20) seen. Strange, sinuous features were observed in the maria. Although various land forms
. g' s& M; X; E& Y# ]. Hwere catalogued, the majority of astronomers’ attention was fixed on craters and their
7 c2 x$ ^2 p' Y) t! ~$ N. p, worigins. y% B2 R& x6 h* H3 `
Astronomers have known for a fairly long time that the shape of craters changes as
s. ]( T$ W R1 C$ [- d+ U# {4 Fthey increase in size. Small craters with diameters of less than 10-15 km have relatively
6 O ]5 |7 k6 }' h9 @% o(25) simple shapes. They have rim crests that are elevated above the surrounding terrain,) ]8 T& E' L* z0 W0 F* S' o3 n: l
smooth, bowl-shaped interiors, and depths that are about one-fifth to one-sixth their diameters. The complexity of shape increases for larger craters.
' M' g) a1 y: e; F % u1 ]& ^% p& I) G4 \
41. What does the passage mainly discuss?
0 f2 @; g5 N" ~" L$ x" EWhat astronomers learned from the Surveyor and Apollo space missions4 q5 R0 I0 l! z8 y! t
Characteristics of the major terrains of the Moon
1 r4 ]; w5 ^# p! O$ {2 OThe origin of the Moon’s craters
# V0 C9 ]& y7 m) gTechniques used to catalogue the Moon’s land forms; l" l8 f" g3 m2 ^
! s1 M) p ~: q3 s% H3 H42. The word ”undergone” in line1 is closest in meaning to 1 k& _& S2 U/ Y4 D8 _
altered1 Y* _- H, d* ~ v
substituted( X. C" B* \) N# ]
experienced& R" q/ `, _/ x8 O8 W; Z, |+ Y
preserved: ?: W1 U8 ]9 B. E& `
! Q* ~' P7 G$ a4 i0 V/ [3 C) ~43. According to the passage, the maria differ from the terrace mainly in terms of 6 M, p& e0 ?# ^4 C, l% }& u3 {
age
' q& t- N# V# I% Dmanner of creation
- F; W( a i' h: \3 esize
! X& w) \4 c' g; o- D" G8 ?composition |