>>4 is right.

The following two sentences are almost the same. But the latter is little stiffer and more formal.

彼女はひらがなが読める。
= She can read Hiraganas.

彼女はひらがなを読むことができる。
= She is capable of reading Hiraganas.

Also, "今、わかるか？" sounds very gaijin.
Native speakers would say "これなら、分かりますか？".