3. Excuse me, are you a volunteer here? 打扰一下，你是这里的志愿者吗?
【感知】(1) Robert wants to be a volunteer too. 罗伯特想成为一名志愿者。
(2) Where do you volunteer? 你在哪里做志愿者?
(3) Many teenagers volunteer to help the elderly. 很多青少年都志愿帮助老年人。
【思考】通过观察可知，volunteer 既可作词，意为“”；也可作词，意为“”，其后可跟动词不定式，表示“”。voluntary 是词，意为“”。
【运用】
(1) Many students volunteer (help) old people on weekends.
(2) They think being a volunteer is meaningful. (英译汉)

思考：名；志愿者；动；志愿，自愿；志愿、自愿做某事；形容；志愿的，自愿的
运用：（1）to help （2）他们认为做志愿者是有意义的。

4. —How long have you been a volunteer? 你做志愿者多久了?
—I have been a volunteer for a few months. 我做志愿者已经几个月了。
【感知】(1) One of my friends has volunteered here for a long time. 我的一位朋友在这里做志愿者很长时间了。
(2) —How long has he volunteered here? 他在这做志愿者多长时间了?
—He has volunteered here since his summer holidays started. 从暑假开始他就在这里当志愿者了。
(3) She has been a volunteer at a nursing home since last August. 她从去年八月就在一家养老院做志愿者了。
【思考】通过观察可知，since 和 for 都可以在现在完成时中表达动作或状态持续的时间。
for 后面跟；since 后面跟或从句，从句时态需使用。在现在完成时中对动作或状态持续的时间提问时，需使用特殊疑问词组。
【运用】
(1) 用 since 或 for 填空。
① Ms Li has been a teacher three years.
② Tom has learnt to play badminton 2000.
③ Teng Fei has been a volunteer at a nursing home he became a middle school student.
(2) — have you been a singer?
—Since two years ago.
(3) I've picked up three bags of bottles since I (arrive) this morning.

思考：时间段；过去的某个时间点；一般过去时；How long
运用：（1）① for ② since ③ since （2）How long （3）arrived