辨析ahead/forward/along

辨析ahead/forward/along
3ahead/forward/along者均做‘向前,往前’（adv）讲时有什么区别吗?下述8个句子里的该3个词都可以互换吗?
1>She bicycled along,singing loudly .(动作方向的'向前')
2>The soldiers crept forward under cover of darkness.(动作的方向性),
3> from this time forward (时间的方向性),
4>The year crept along unnoticed.(时间的方向),
5>The line of cars moved ahead slowly.(动作的‘向前’）
6>Full speed ahead.
7>Police have appealed for witnesses to come forward.
警方呼吁目击者挺身而出.
8>The policeman told the crowds to move along.
警察叫人群向前走动.

总说：一般来说,ahead/forward在表示“向前(时间,空间)”的意思时,一般没有区别,但固定搭配不在此列；而与along有细微区别,along含有一直向前的意思.
1>She bicycled along,singing loudly .(动作方向的'向前')
==>along/ahead/forward都可以.along/ahead/forward都可以.但意思有些许差异,along强调“延续向前或继续向前”,ahead/forward只有向前的意思.
She bicycled along,singing loudly.她骑着自行车,沿途大声唱歌.
She bicycled ahead/forward,singing loudly.她骑着自行车,在大声唱歌(可能只在汽车过程中唱了一句).
2>The soldiers crept forward under cover of darkness.(动作的方向性),
==>along/ahead/forward都可以.辨析同上.
3> from this time forward (时间的方向性),
==>ahead/forward/along都行.
from this time along从此刻向前的一段时间(一段时间)
from this time forward/ahead此刻以前(时间点)
4>The year crept along unnoticed.(时间的方向),
==>along/ahead/forward都可以.但意思有些许差异,along强调“延续向前或继续向前”,ahead/forward只有向前的意思.
The year crept along unnoticed.时间一直在偷偷向前.
The year crept forward/ahead unnoticed.时间偷偷向前.
5>The line of cars moved ahead slowly.(动作的‘向前’）
==>along/ahead/forward都可以.但意思有些许差异,along强调“延续向前或继续向前”,ahead/forward只有向前的意思.
The line of cars moved ahead/forward slowly.汽车慢慢向前行驶.
The line of cars moved along slowly.汽车一直慢慢向前行驶.
6>Full speed ahead.
==>辨析同上.
full speed ahead/forward全速向前
full speed along一直在全速向前(以前就在全速向前,现在还在全速向前)
7>Police have appealed for witnesses to come forward.
警方呼吁目击者挺身而出.
==>固定搭配.come forward自告奋勇；come along出现,发生,陪伴；没有come ahead的说法.
8>The policeman told the crowds to move along.
警察叫人群向前走动.
==>along/ahead/forward都可以.但意思有些许差异,along强调“一直向前”,ahead/forward只有向前的意思.