C.
對(duì)次數(shù)提問(wèn),有兩種,
1.how often
2.how many times
how long有以下兩個(gè)主要意思：
1.表示多長(zhǎng)時(shí)間,主要用來(lái)對(duì)一段時(shí)間(如three days,four weeks 等)提問(wèn).如：
A：How long did he stay here?他在這兒呆了多久?
B：About two weeks.大約兩個(gè)星期.
A：How long does it take to get to London from here?從這里到倫敦要多長(zhǎng)時(shí)間?
B：At least ten hours.至少要10個(gè)小時(shí).
2.表示某東西有多長(zhǎng).如：
A：How long is the river?這條河有多長(zhǎng)?
B：About 500 km.大約500千米.
二、how often的用法
how often 指每隔多久,主要用來(lái)對(duì)頻度副詞或狀語(yǔ)(如：once a week,three times a month 等)提問(wèn).如：
A：How often does he come here?他(每隔)多久來(lái)一次?
B：Once a month.每月一次.
A：How often do you visit your mother?你多長(zhǎng)時(shí)間看你媽媽一次?
B：Once a week.一周一次
how long 是對(duì)時(shí)間多久的提問(wèn).