单 元：unit 1 tales of the unexplained
板 块：grammar and usage 2
thoughts on the design:
learn the differences between the present perfect tense and the present perfect continuous tense.
teaching objectives:
1. learn how to form and use the present perfect tense.
2. understand when the present perfect continuous tense is used in sentences.
teaching procedures:
step 1 compare the two tenses
1. we use the present perfect tense to talk about an action completed in the recent past, and the present perfect continuous tense for an action that started in the past and is still happening.
现在完成时和现在完成进行时都表示动作从过去开始，但现在完成时可表示事件或动作刚结束，而现在完成进行时则强调动作仍在继续。
1) li jia has read a book about stonehenge. （表示她已经读完了。)
2) li jia has been reading a book about stonehenge. (表示她仍在读。)
2. we can use the present perfect tense for repeated actions, and the present perfect continuous tense for non-stop actions.
we usually use the present perfect tense to ask questions beginning with how many/much, and the present perfect continuous tense to ask questions beginning with how long.
现在完成时可表示反复发生的动作，提问时用how many / how much。而现在完成进行时则表示持续的、不间断的动作，提问时用how long。
1) —how many times have you visited egypt this month? 你这个月去了埃及几次？
—i have visited egypt twice this month. 我这个月去了埃及两次。
2) —how long have you been touring egypt? 你在埃及旅游多久了？
—i have been touring egypt for two months. 我已经在埃及旅游两个月了。
3. we can use either a state verb or an action verb with the present perfect tense but we usually can only use an action verb with the present perfect continuous ten
