221. There are 5 ________ in the passage about nanometer(纳米) technology we have just read. Please tell me the general meaning of the first one.
There are some health problems that, when ________ in time, can become bigger ones later on.
In April thousands of holidaymakers remained ________ abroad due to the volcanic ash cloud.
Film has a much shorter history, especially when ________ such art forms as music and painting.
When ________ for his views about his teaching job, Philip said he found it very interesting and rewarding.
Even the best writers sometimes find themselves ________ for words.