regret doing/to do
regret to do 对要做的事遗憾。 （未做）
regret doing 对做过的事遗憾、后悔。 （已做）
I regret to have to do this, but I have no choice.
I don't regret telling her what I thought.
——You were brave enough to raise objections at the meeting.
——Well, now I regret ___ that.
A. to do B. to be doing C. to have done D. having done
答案：D.regret having done sth. 对已发生的事感到遗憾。regret to do sth. 对将要做的事感到遗憾。本题为对已说的话感到后悔，因此选D.
感官动词 + doing/to do
感官动词 see, watch, observe, notice, look at, hear, listen to, smell, taste, feel + do 表示动作的完整性，真实性；+doing 表示动作的连续性，进行性
I saw him work in the garden yesterday.
I saw him working in the garden yesterday.（强调"我见他正干活"这个动作）
1）They knew her very well. They had seen her ___ up from childhood.
A. grow B. grew C. was growing D. to grow
答案：A.因题意为，他们看着她长大，因此强调的是成长的过程，而非正在长的动作，因此用see sb do sth 的句型。
2）The missing boy was last seen ___ near the river.
A. playing B. to be playingC. playD. to play
答案A. 本题强调其动作，正在河边玩，应此用see sb. doing sth句型。