帮忙看一下这段Abap的程序，请写一下注释，有点看不明白

Question

PARAMETERS p_cityfr TYPE spfli-cityfrom DEFAULT 'Frankfurt'.

DATA: wa_carrid TYPE spfli-carrid,
wa_connid TYPE spfli-connid,
wa_carrname TYPE scarr-carrname.

DATA: t1 TYPE i,
t2 TYPE i,
time TYPE i,
n TYPE i VALUE 1000.

* Processing Blocks

START-OF-SELECTION.

DO n TIMES.
GET RUN TIME FIELD t1. “这个地方是在干嘛？
* ----------------------------
SELECT carrid connid ”这个select的是一行数据还是别的什么
FROM spfli
INTO (wa_carrid, wa_connid)
WHERE cityfrom = p_cityfr.
SELECT carrname
FROM scarr
INTO wa_carrname
WHERE carrid = wa_carrid.
...
ENDSELECT.
ENDSELECT.
* ----------------------------
GET RUN TIME FIELD t2.
time = time + t2 - t1.
ENDDO.

WRITE: 'Runtime:', time.

Answer 1

* 输入框，这个没问题吧
PARAMETERS p_cityfr TYPE spfli-cityfrom DEFAULT 'Frankfurt'.

* 声明变量
DATA: wa_carrid TYPE spfli-carrid,
wa_connid TYPE spfli-connid,
wa_carrname TYPE scarr-carrname.

* 继续声明变量
DATA: t1 TYPE i,
t2 TYPE i,
time TYPE i,
n TYPE i VALUE 1000.

* 主事件块
START-OF-SELECTION.

* 执行1000次循环
DO n TIMES.
GET RUN TIME FIELD t1. “获取程序运行到这里时所用的时间，单位为微秒

* carrid和connid是spfli表的两个字段，分别是航班号和飞行连接数，是
* 德语的缩写。将符合条件的字段取出来放入work area工作区中。
* carrname是航班名称
SELECT carrid connid
FROM spfli
INTO (wa_carrid, wa_connid)
WHERE cityfrom = p_cityfr.
SELECT carrname
FROM scarr
INTO wa_carrname
WHERE carrid = wa_carrid.
...
ENDSELECT.
ENDSELECT.
* ----------------------------
GET RUN TIME FIELD t2. “获取程序运行到这里时所用的时间，单位为微秒
time = time + t2 - t1.
ENDDO.

WRITE: 'Runtime:', time.“打印程序运行总时间

over！