妈妈在骂马吗？
－ing是进行时

但是这句五个字的发音全是 ma，如果加一个「在」字进去，就好像没那么有趣了 :-P

我只是从意思上说的，“妈妈骂马吗？”应该是Does mother scold the horse?

congcong小姐，我看您太严肃了。

在很多情况下，用现在一般时表示进行时也可以吧。　例如：

你去哪儿？　Where are you going?
干啥？ What are (you) doing?
你去北京干啥？ What are you going to Beijing for?
-妈妈在干什么？　-做饭。　What's Mom doing? Making dinner.

而且，这句话千万不许改变。其他的都可以，因为他们都是这句的翻译。

Also, I don't know if this counts as a "tongue twister". Tongue twisters are hard to say (i.e. finish the sentence), but this is just one word: "ma". It's for practicing tones, which doesn't twist the tongue, as far as I know.

好吧，随你便

I was the one who tagged it «tongue twister».

If you look up «mandarin chinese tongue twisters» in Google, you find many of these these that are for practicing tones [1]. The number of sites citing this phrase in the form you're added is small[2], but there are a number of sites that list variations of this phrase[3].

The fact that you don't have to twist your tongue isn't important in this case. ^^ After all, «tongue twisters for practicing tones» is nowhere as strange as Russian «синие чернила»[4].

[1] http://www.google.com.by/search...ongue+twisters
[2] http://www.google.com.by/search...AC%E5%90%97%22
[3] http://www.google.com.by/search...&start=80&sa=N — 43 results
[4] Чёрные чернила Rus. «blue ink», literally ~ «blue blackener»

Thank you for the detailed and in-depth explanation.

He-he, you're always welcome! ;)