在含有if条件状语从句的复合句中，如果主句为下列情况，从句要用一般现在时。
（1) 主句为一般将来时
（2) 主句为祈使句
（3) 主句含有情态动词
eg：If your head and neck still hurt tomorrow,then go to a doctor.
如果明天你的头和脖子还痛的话，就去看医生吧。
分析：本句是含有条件状语从句的复合句，主句是 then go to a doctor, 从句是if your head and neck still hurt tomorrow,if是连词，意为"如果，假如"、引导条件状语从句。
If you need help,just let me know.
如果你需要帮助，就告诉我。
If it rains tomorrow,we won't go to the park.
如果明天下雨，我们将不去公园。
You should take a break if you are tired.
你如果累了，就应该休息一下。
－Do you think if Robert will go to the zoo tomorrow?
－I think he will go if he_____ too much homework.
A.don't have
B.won't have
C.doesn't have
解析：在含近f引导的条件状语从句的复合句中，如果主句用一般将来时，则从句用一般现在时表将来。故选C.
