他們肯定是迷路了，不然他們應該已經到了很久了。

They lost their way; otherwise, they would have arrived long ago.

Source: Tatoeba

Sentence Composition

1 他們 tāmen they; them
2 肯定 kěndìng
  1. to be certain; to be positive
  2. assuredly; definitely
  3. to give recognition; to affirm
  4. affirmative (answer)
=3 是 shì
  1. to be (followed by substantives only)
  2. correct; right; true
  3. (respectful acknowledgement of a command) very well
  4. (adverb for emphatic assertion)
=3 是 shì variant of 是 shì
4 迷路 mílù
  1. to lose the way
  2. lost
  3. labyrinth
  4. labyrinthus vestibularis (of the inner ear)
=5 了 le
  1. (completed action marker)
  2. (modal particle indicating change of state, situation now)
  3. (modal particle intensifying preceding clause)
=5 了 liǎo
  1. to finish
  2. (used with 得 dé or 不 bù after a verb to express (im)possibility, as in 忘不了 wàngbuliǎo "cannot forget")
  3. (literary) (usually followed by a negative such as 无 wú or 不 bù) completely (not); entirely (not); (not) in the least
  4. to understand clearly (variant of 了 liǎo)
=5 了 liǎo
  1. (of eyes) bright
  2. clear-sighted
  3. to understand clearly
=5 了 liào unofficial variant of 瞭 liào
6 不然 bùrán
  1. not so
  2. no
  3. or else
  4. otherwise
  5. if not
  6. How about ...?
7 他們 tāmen they; them
8 應該 yīnggāi ought to; should; must
9 已經 yǐjīng already
10 到了 dàoliǎo
  1. at last
  2. finally
  3. in the end
11 很 hěn
  1. very; quite
  2. (also, often used before an adjective without intensifying its meaning, i.e. as a meaningless syntactic element)
12 久 jiǔ (of a period of time) long
=13 了 le
  1. (completed action marker)
  2. (modal particle indicating change of state, situation now)
  3. (modal particle intensifying preceding clause)
=13 了 liǎo
  1. to finish
  2. (used with 得 dé or 不 bù after a verb to express (im)possibility, as in 忘不了 wàngbuliǎo "cannot forget")
  3. (literary) (usually followed by a negative such as 无 wú or 不 bù) completely (not); entirely (not); (not) in the least
  4. to understand clearly (variant of 了 liǎo)
=13 了 liǎo
  1. (of eyes) bright
  2. clear-sighted
  3. to understand clearly
=13 了 liào unofficial variant of 瞭 liào