Key调:

why do we call it a "sonata in C major" ,or say that "it's written in the key of C"?
Most people would answer that music is "in a key" when its tones relate to one central tone(the one that has the same nme as the key)and when the functions of the other tones results from the keys in which they relate to the central one.
According to this answer ,the Morart Sonata is in C because C is the central tone;we hear the other tones as subordinate ([sə'bɔːdɪnət]附属)to C.

The Tonic主音:

Word：prominent突出的 bars小节（线） downward向下的 subsequent 后来的sixteenth-note 十六分音符scales音阶 repeat重复 generalizing from总结
We can state that the tonic,the central tone of the key,forms the point of departure (出发)from which the other tones move and the goal to which they are directed.
主音（调的中心音），不仅是其他音移动的出发点（the point of derarture），并且也是其他音朝向的目标。

Word:pieces contain包含subordinate从属的tonal ['təʊn(ə)l]音调的consecutive连续的 [kən'sekjʊtɪv] symbol ['sɪmb(ə)l]标志abstraction抽象的cap加盖，帽子throughout贯穿始终pitch音高
For the most part the pieces would contain the tones C,D,E,F,G,A,and B,and any other tones would paly a subordinate role.
别的C大调的乐曲也都会包括CDEFGAB,并且别的音都扮演着从属/次要的角色。
When all the tone that belong to a key occur in consecutive order ,each one next to those closest to it in pitch,the result ia s scale.
当所有的属于一个调的音按照连续的顺序来排列，音高相邻的音排列在一起，结果就是音阶。
1:Tonic.2:supertonic.3:mediant.4:subdominant.5:dominant.6:submediant.7:leading tone。

word:register ['redʒɪstə]音域 indicate equivalent相等的
The beginning and ending tones of Example 1-4 are both C,but they are not one and the same tone.The last tone sounds considerably(非常的)higher in pitch than the first.Yet ,despite this marked(明显的) difference in register, the sounds of two C's are very similar,that's why we call them both by the same letter name.When two tones are separated by an octave they are equivalent-----that is ,they are variants(变体) of the same sound.
This phonomenon of the octave ['ɒktɪv] equivalence is one of the most important aspects of pitch organization in music.In technical writing about music,it is frequently helpful to indicate the register in which a tone occurs.
这个八度等音调现象是音高组织中最重要的概念之一。在音乐写作中，它对指出音所在的音域非常有帮助。
其实是说我们学过的小字一组，大字组.....都是根据八度划分界限和分组的。（猜测WHY小字1组是c是因为c正好在高音谱号的第一线/个）
小字一组（c1）：one-line.二组：two-line..... 小字组（低音c）：small.大字组：great.再低大字一组（C1）:contra。大字二组：sub-contra

adjacent 相邻的

The distance between one tone of a scale and the next is usually called a step级/阶.
The scale from C to C contains two kinds of steps: small ones betwwen E and F and betweenB and C,larger ones between the other adjacent tones. we call the smaller steps half steps(semitones)h半音 and the larger ones whole steps(or whole tones)w全音.

applied V and VII副属和副导
Any major or minor triad ['traɪæd] may be preceded[prɪ'siːd] by an applied V or VII(tirad or seventh-chord).
When the cross relation is between adjacent[ə'dʒeɪs(ə)nt]邻近的 upper voices in the same register.
In sequences模进 with descending 5ths,a chainl链子，连接一串 odf applied chords is possible连续下行,each sounding like the dominnant of the next.