The Moon, which has undergone a distinct and complex geological history, presents a7 ~3 Z% K# V; l; n. B
striking appearance. The moon may be divided into two major terrains: the maria (dark
; y/ t8 m% }# Q, zlowlands) and the terrace( bright highlands). The contrast in the reflectivity (the capability
6 w# O4 J I3 _: W9 F8 g' c5 P2 b: Lof reflecting light ) of these two terrains suggested to many early observers that the two
# t5 _8 p0 N9 j/ z9 P# P) f- J(5) terrains might have different compositions, and this supposition was confirmed by * e8 ~8 v2 M4 ~) i$ t
missions to the Moon such as Surveyor and Apollo. One of the most obvious differences1 I) J ]& K, ^
between the terrains is the smoothness of the maria in contrast to the roughness of the
5 b0 f% o4 [% \* G0 r: Khighlands. This roughness is mostly caused by the abundance of craters; the highlands are
, \- D) f2 |2 V/ _1 r N4 wcompletely covered by large craters( greater than 40-50 km in diameter), while the craters 6 c* N* A2 L. U; Z9 q& c
(10) of the maria tend to be much smaller. It is now known that the vast majority of the Moon’s
% c2 F) g5 {$ ?: Dcraters were formed by the impact of solid bodies with the lunar surface.9 `; N/ y9 f @
Most of the near side of the Moon was thoroughly mapped and studied from telescopic: P% Z7 t) Z: c2 Z
pictures years before the age of space exploration. Earth-based telescopes can resolve
" t! L% q6 M; u) w% b c8 l* jobjects as small as a few hundred meters on the lunar surface. Close observation of 6 }& O! z) Y3 ]- t, g' }
(15) craters, combined with the way the Moon diffusely reflects sunlight, led to the
# m* D* W" @) w! {8 U$ D4 punderstanding that the Moon is covered by a surface layer, or regolith, that overlies the
0 n9 J, n K' j, X5 ?9 nsolid rock of the Moon. Telescopic images permitted the cataloging of a bewildering array* P8 v5 p W4 Q$ i
of land forms. Craters were studied for clues to their origin; the large circular maria were+ P K6 x$ j, F5 c) G
(20) seen. Strange, sinuous features were observed in the maria. Although various land forms5 F/ Q! P; A4 U P
were catalogued, the majority of astronomers’ attention was fixed on craters and their & D) s8 c! \6 M3 l8 }$ d' {5 F
origins.
, N. R) Y# ~4 U4 a/ S% I5 _ Astronomers have known for a fairly long time that the shape of craters changes as+ a; p u3 W4 D" N1 Z s+ ^
they increase in size. Small craters with diameters of less than 10-15 km have relatively " Y/ b( ~+ m* @
(25) simple shapes. They have rim crests that are elevated above the surrounding terrain,
7 e5 n. t1 V5 X, G# h, n- `4 O# Hsmooth, bowl-shaped interiors, and depths that are about one-fifth to one-sixth their diameters. The complexity of shape increases for larger craters.
& V0 v9 G/ l7 O& D2 M6 Z4 d: G & N$ u; J& N/ t1 d/ T* x& d
41. What does the passage mainly discuss?9 T& g# S! t. @. ^
What astronomers learned from the Surveyor and Apollo space missions# L% n" @/ M& d: u4 f! Q! w& O
Characteristics of the major terrains of the Moon( n, f& j& z6 y/ \8 A4 e
The origin of the Moon’s craters' a" d3 \" d) e4 g: R6 F
Techniques used to catalogue the Moon’s land forms
3 K+ E& v- n; E/ F( H5 c: Z {7 F0 S# K: Q/ U* { J8 T
42. The word ”undergone” in line1 is closest in meaning to 0 s) L) I. @6 h) O
altered1 o, \5 u# r$ s1 M$ g9 n; S
substituted
4 V/ K1 D( m6 ]experienced
' p6 t7 s" N `preserved# R: E$ l0 B+ y) N6 z
7 D: g3 l$ T+ |! \6 O* K43. According to the passage, the maria differ from the terrace mainly in terms of
+ m. \5 u. [; R/ c* w: u' mage
) c* x* m" h6 p e9 q% I- V4 Z; cmanner of creation
- @& J# J9 d4 msize
1 X( D% U1 k: r& _! i3 Gcomposition |