課文這樣寫道: Have you ever seen the moon slowly begin to darken and turn a red color for a few hours? 請問句中,應該用begin還是beginning呢?

請問句中,應該用begin還是beginning呢?
應該用begin, 因為較配合全句意思 (两個不能同時進行的動作).
如果分開两個動作去問,就可以用分詞.
例如:
1. Have you ever seen the moon beginning to darken?
2. Have you ever seen the moon slowly turning red?

Analysis for the phenomenon of a lunar eclipse (total):
1. the moon starts to darken (when it is passing through the Earth's shadow)
2. then it changes its colour into red (when it crosses entirely into the Earth's umbra 本影)
3. the moon starts to brighten again
3. the whole process could take several hours to complete

The question -
Have you ever seen the moon slowly begin to darken and turn a red color for a few hours?
is more or less equivalent to asking
Have you ever seen the whole process of a total lunar eclipse?

What we know -
1. after the verb of perception such as "see", we can use either the bare-infinitive or present participle to follow the object, but they have different meaning;
2. inf. means witnessing the whole event;
3, pp. means witnessing the action in progress (that is, the action in progress is intercepted by the action of "see")

「現在分詞」和「不定詞」在做「受詞補語」時，意義不同：
I saw him "changing" the wheel.表示動作的現在分詞，它的動作可以是「全程」或「部分」。
即我看到他換輪胎的「全部」或「部分」行動。
I saw him "change" the wheel.表示動作的不定詞，它的動作是「全程」的。
即我看到他換輪始的「全部」行動（重開始到結束）。

按字義，begin的動作是發生在瞬間的，是一個「點」，不是一個「過程」。開始就開始了。所以我們看到某件事begin時，「不能」也「不必」強調看到的開始是「全程」或「一部分」。所以用「不定詞」較合理。因為「現在分詞」會有正在進行中的意思，不合理。

兩者都可以,
begin是開始
beginning是正在開始