A.1/2波長(zhǎng)的整數(shù)倍時(shí) B.1/2波長(zhǎng)的奇數(shù)倍時(shí) C.1/4波長(zhǎng)的奇數(shù)倍時(shí) D.1/4波長(zhǎng)的整數(shù)倍時(shí)