In how many ways can 21 identical English and 19 identical Hindi books be placed in a row so that no two Hindi books are together?

In how many ways can 21 English and 19 Hindi books be placed in a row so that no two hindi books are together?

In how many ways can 21 identical white balls and 19 identical black balls be arranged in a row so that no 2 black balls are together?

In how many ways can 19 indentical books on English and 17 identical books on Hindi be placed in a row on a shelf so that two books on Hindi may not be together ?

In how many ways can 10 identical shirts and 7 identical trousers be placed in a row on a shelf so that two trousers may not be together ?

In how many ways can 10 identical shirts and 7 identical trousers be placed in a row on a shelf so that two trousers may not be together ?

In how many ways can 21 books on English and 19 books on Hindi be placed in a row on a shelf so that two books on Hindi may not be together? (A) 770 (B) 385 (C) 1540 (D) 399